Contrary to mouse clicks, when pressing keys on a keyboard the
standard behavior is to perform the associated action immediately,
not only when releasing the key again. This should also improve the
perceived performance slightly.

Note that the 'D' shortcut had formerly been handled by Leaflet, which
we now have to do on our own.

While at it, move the character codes over to the options variable, as
found in other parts of the codebase already.

Also removing the listener from the container does not seem needed
anymore nowadays.

Those shortcuts were already working before, but not really
discoverable for users.

To achieve a consistent UI and keep the wording in line with existing
conventions and future shortcuts (i.e. no whole sentences, shortcut in
parenthesis), the mute tooltip is changed again to occupy two lines (to
limit the width of the tooltip), to be less wordy (so it is faster to
read), to use the "mute" term (to help memorizing the M shortcut, at
least in English), and to align with the parenthesis style.

Do not allow browser keyboard shortcuts to trigger route functions,
e.g. pressing Ctrl+P triggers printing in most browsers, but should not
at the same time switch BRouter-Web to POI mode. This can be prevented
by filtering for modifiers.

In the same fashion, when modal dialogs or dropdowns are open it should
not be possible to activate map functions in the background now.

Finally, inhibit shortcuts in number input fields too, as found in the
editable number input fields in the customize profile options.
Previously only regular text input fields were protected.

To make those checks easier to use, they are deduplicated and moved to
Util.js.

The mute shortcut would only work for regular routes before.

Note that no-go areas, POIs and tracks continue to be unaffected
by muting, so e.g. peeking at a track below the route is still possible.

Press 'C' repeatedly to switch between the various color coding options.
When the last one is reached, we show the regular route again.

Press 'L' to initiate the "Show me where I am" function.

It was not translated before, since the string was coming from an
external dependency.

Press 'F', type a query and press 'Enter' to find places effortlessly.

Note that the button already triggers on mousedown events, even though
by convention it should react on mouseup (i.e. a regular click)
only. However, that's an issue in the external dependency, and can
be worked around for now.

Press 'R' to swap start and end of the route.

Press 'N' to initiate drawing a no-go area. 'Escape' will cancel,
similar to how drawing a route works.

Press 'Z' to undo adding the last point.

Prevents "Uncaught TypeError: Cannot read property 'off' of null"
in L.Routing.js

Use 'Backspace' to show the dialog allowing to clear the route.

The 'Del' key could then be used in the future to possibly allow to
delete individual selected items like POIs or no-go areas.

Press 'S' to show the Strava buttons (if the API key has been set) as
well as the Strava segments layer (once it has been fetched).

Note that fetching and updating data from Strava still needs to be
triggered manually by clicking the respective biking or running button.

Press 'G' to open the profile switcher, select a profile with the arrow
keys, apply with 'Enter' and close the switcher with 'Escape'.

While 'T' and 'P' will be / were already taken, 'G' is at least easily
reachable with the left hand for users using a mouse with their right
hand at the same time.

Since Bootstrap keeps updating the tooltip when changing options in the
dropdown (which is useful in case the text is longer than the width of
the control), the shortcut text needs to be applied dynamically too.

Press 'X' to trigger the export route dialog.

Automatically populating the trackname field should work too.

Press 'O' or 'Shift+O' to open/load tracks or no-go areas respectively.

Press 'H' to get to the helpful about dialog.

The 'T' key will show/hide the most recent sidebar tab.

Pressing 'Shift+T' will switch to the next sidebar tab, possibly
wrapping around to the first tab.

If the Itinerary tab is hidden, it will be skipped.

Press 'E' to show/hide the elevation chart.