Add custom bitmap marker

[sleepnova]

Setting custom icons for markers as well as showing bubble window with description.

[ecgreb]

The ability to draw custom icons at runtime was recently added as a feature to Tangram ES but it still needs Android bindings. Stay tuned for this one as it should be arriving soon.

tangrams/tangram-es#930

We don't have anything like a "bubble window" in the pipeline as it stands now although you can set a callback on markers and implement any sort of custom behavior you want.

[ecgreb]

Tangram ES branch with dynamic marker API is here https://github.com/tangrams/tangram-es/tree/android-marker

[ecgreb]

Tangram pull request is here and has been approved (waiting for merge).

tangrams/tangram-es#1056

Worth noting is that there is still work outstanding to make the new markers selectable and so this capability won't be available in the SDK right away.

[ecgreb]

#340 implements adding and removing a dynamic marker based on a drawable resource ID. Currently position, resource ID, and style string are configurable.

Additional work includes:

• Set marker icon using a Drawable object rather than from a resource ID (Create custom bitmap marker using a Drawable object #342)
• Make marker size configurable without using a style string. For example MarkerOptions.size(width, height) should modify the style string width and height pixel values (Marker size should be configurable without setting entire style string #343)
• Add ability to modify marker position, icon, and visibility once created (Modify marker position, icon, and size after creation #344)
• Restore markers on rotation if map is set to persist data (Restore custom markers on rotation #348)