Display bottom panel when in fullscreen mode

[jbaiter]

For some reason the bottom panel is disabled when Mirador is in fullscreen mode, making navigation pretty tedious. This PR removes the calls to disable the bottom panel in fullscreen mode.

[coveralls]

Coverage decreased (-0.2%) to 61.618% when pulling 9a01021 on dbmdz:bottompanel-in-fullscreen into b4248b4 on ProjectMirador:2.1.3.

[coveralls]

Coverage increased (+0.05%) to 61.835% when pulling 6a23781 on dbmdz:bottompanel-in-fullscreen into 099324d on ProjectMirador:2.1.3.

[coveralls]

Coverage increased (+0.05%) to 61.511% when pulling 4388825 on dbmdz:bottompanel-in-fullscreen into 993b08e on ProjectMirador:2.1.4.

[aeschylus]

Let's take this up on the call this Thursday. I remember this was requested at one point, so perhaps it's worth making this a configuration option.

Additionally, it might do to improve the responsiveness of the bottom panel so that it isn't so tiny on large displays. The size also causes many more thumbnails to need to load than may really be necessary for the user to navigate right off the bat.

For now I'll mark this as a won't fix.