Contacts theming

[sowjanyakch]

This PR is continuation for PR #3936.

• Image caching for user avatars.
• Theming for composable activity (this is partially implemented and I see only white color is applied to components in dark mode and black color is applied to components in light mode. Need to investigate what's causing this issue)
• unit tests for viewModel.

🚧 TODO

• ...

🏁 Checklist

• ⛑️ Tests (unit and/or integration) are included or not needed
• 🔖 Capability is checked or not needed
• 🔙 Backport requests are created or not needed: /backport to stable-xx.x
• 📅 Milestone is set
• 🌸 PR title is meaningful (if it should be in the changelog: is it meaningful to users?)

[mahibi]

fine for me. just rebase and squash to get rid of the old commits which code is already in master...

[mahibi]

conspicuous/known issues:

• the status bar should be aligned to the other colors
• the category letters are blue but should be themed
  (can be done in followup PRs, more important is to focus on functionality at create conversation screen for now)

[github-actions]

Codacy

Lint

Type	master	PR
Warnings	90	84
Errors	129	131

SpotBugs

Category	Base	New
Bad practice	6	6
Correctness	11	11
Dodgy code	78	78
Internationalization	3	3
Malicious code vulnerability	3	3
Performance	6	6
Security	1	1
Total	108	108

Lint increased!

[github-actions]

APK file: https://www.kaminsky.me/nc-dev/android-artifacts/4011-talk.apk



To test this change/fix you can simply download above APK file and install and test it in parallel to your existing Nextcloud Talk app.