Add "Favorite Chats" category to the chat selector screen

[jrichardsen]

Fixes #47

[codecov]

Codecov Report

Attention: Patch coverage is 76.54321% with 19 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/backend/nc_talk.rs	11.1%	8 Missing ⚠️
src/ui/widget/chat_selector.rs	88.4%	8 Missing ⚠️
src/backend/nc_room.rs	0.0%	3 Missing ⚠️

Files with missing lines	Coverage Δ
src/backend/nc_room.rs	63.9% <0.0%> (-0.8%)	⬇️
src/backend/nc_talk.rs	79.0% <11.1%> (-1.1%)	⬇️
src/ui/widget/chat_selector.rs	94.6% <88.4%> (-2.6%)	⬇️