Popup UI needed to set various user preferences + integration with custom elements suite

[ahmadayubi]

If there are user preferences anyone feels are needed feel free to discuss about it below.

A mechanism is also needed to allow the stored preferences to be used within the custom elements suite.

One solution is to inject a script the custom element interacts with to set it's internal variables. For this the run_time needs to be set to document_start (this does have performance concerns and isn't preferred).

Another alternative is to use the external messages functionality or the connect function described here. The drawback is that you cannot listen for external communication from any website, i.e. no wildcards option allowed for externally_connectable

Currently requested preferences:

• Button size
• Ability to reduce or turn off pan/zoom animations
• Enable/disable announcing of zoom + location on zoom and moveend for screen readers #11

[Malvoz]

People with vestibular disorders may want the option to reduce or turn off animations, such as pan/zoom animations.
(Related WCAG Success Criteria: 2.3.3 Animation from Interactions.)