Version 2.5-beta1

Changes since

* update ical4j: now allows UTC properties to have non-UTC values for compatibility
* use AndroidX Room for database access
* AccountActivity reworked
  - use tabs for CalDAV/CardDAV/Webcal
  - use RecyclerView, PagedList adapter and Room observeable queries for best performance even with huge lists
  - progress bars now also show pending syncs
* DavService: don't delete all homesets/collections on refresh, but update only changed rows
* vCard: use "groupX" instead of "davdroidX" for property grouping
* use Conscrypt to bring modern TLS versions/ciphers to all supported Android versions
* many small improvements and bug fixes
This tag has no release notes.