Adds a button in the StickerScreen header to set a sticker as tray icon.
We use tray icon from backend which does not initialize tray icon by default at the moment. So it will be also not initialized when uploading the first sticker, this could be added later.
Sticker previews in HomeScreen adjusted so that the first sticker is not skipped anymore. This would hide the first sticker if another sticker is set as tray icon.
Important: Merge #113 first, this branch is based onmvp-screen-changes
, actual diff: https://github.com/brian2509/kangaroo/compare/mvp-screen-changes...tray-icon-appCloses #95, Closes #83