Sync implementation for subscriptions, tracking subscription removals, add fcast link to cast tutorial description.

Fixed crash on Android 10 related to showing and hiding system UI when entering fullscreen. Made Platform comments the default.

Support for cache in reconstructions, non-required cache added to exports, playlists shares now add a cache aswell for quicker importing

Added scroll to top. Full scrollable parent comment and Polycentric process secret backup and automatic database recovery.

Refs, Dev portal improvements and on-device testing, Fix crashes on disabling v8 race conditions, edgecase where history could be null, issue on starting Grayjay with an url

Additional warnings for reinstall, disable uninstall if doesn't make sense, reduce maxheight to 40% of videoview

Added ability to click on a comment to view where the comment was placed and the ability to navigate upwards in the replies overlay by clicking the parent comment.

Added icon based on the system key when a polycentric user has not set a profile picture. Made managing Polycentric profile most robust. Fixed an issue where latest events were not always being shown in relation to Polycentric profiles. Added copyable (on long press) system key in Polycentric profile activity. Added tutorial videos tab and flow.