remove hardcoded access token

[cammace]

Before this repo goes public, the hardcoded access token should be removed from the testapp and the gradle script for creating developer_config.xml file added.

cc: @zugaldia @Guardiola31337

[zugaldia]

The token needs to be rotated too.

[tobrun]

This was copied from mapbox-demo, no actions needed there?

[zugaldia]

Yes. It needs to be removed (and rotated) from the demo app repo too. Ticketed in mapbox/mapbox-android-demo#291.

[zugaldia]

I've removed the token with c0d965c. We still need to bring the developer token plugin before being able to close this ticket.

[zugaldia]

Fixed in #24.