Add Map-level Data and Macro Storage

[melek]

Is your feature request related to a problem? Please describe.
Sometimes I want to store data specific to a map such as token positions, macros to change the map from day to night, GM notes to assist with the encounter, VBL/MBL data for altering the map, and more. For a standalone map I want to share, I'd like to include author information, art attribution, and possibly other properties to the map.

I want this data to be exported with the map so it would be retained with the map in any campaign.

Describe the solution you'd like
I want data and macros to be available at the map level, like a 'Map' token. With #1422 and #3077 coming, I want to leave implementation up to the imagination of the developers.

Conventionally I would expect the following out of the feature:

• A 'Map → Map Properties' option for each map. These properties would be accessible with get/setMapProperty functions.
• A 'Map' macro panel, which could be found with a macro link like "MacroName@MAP". I would think these would behave like the GM panel.

It would be neat if the new Library Add-ons would use their own property namespace, and that would automatically have metadata which could let users know which library add-ons/versions the map has embedded data from.

It also would be nice for imported maps (dd2vtt) to have, so the import JSON (replacing the image key with the asset ID for the background image) could be stored directly on the map's own datastore.

Describe alternatives you've considered

• Create a 'Map Data and Macros' token (or tokens) on the map to serve this function. I do this with my Lib:Elevation library and it works okay, but it is not as accessible as a baked in option would be for a variety of reasons. A standard solution would be preferable.
• Create a library which creates such a token automatically and creates a panel to simulate a macro panel which can be docked separately. I played with this and it isn't too hard, but it would need a lot of work and of course add-ons have limited adoption.

Additional context
May dovetail well with #2687, #2333, #3110.