Features:
* Added GIF support for preview images (ntfy-android#76, thanks to @MichaelArkh)
* Added WebP support for preview images (ntfy-android#81, thanks to @jokakilla)
* Added UnifiedPush distributor selection support (ntfy-android#137, thanks to @p1gp1g)

Bug fixes + maintenance:
* Remove REQUEST_INSTALL_PACKAGES permission (#684)
* Request to ignore battery optimizations before receiving subscription (ntfy-android#97, thanks to @p1gp1g)
