Fetch messages in background

[rapterjet2004]

• fixes Fetch messages in background when unread messages are detected in conversation list #4381

Fetches messages and saves them when refreshing the conversation list. Only refreshes what is needed, to save battery.

🏁 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?)

[github-actions]

APK file: https://www.kaminsky.me/nc-dev/android-artifacts/4475-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.

[github-actions]

Codacy

Lint

Type	master	PR
Warnings	94	157
Errors	132	76

SpotBugs

Category	Base	New
Bad practice	6	6
Correctness	16	16
Dodgy code	71	71
Internationalization	3	3
Malicious code vulnerability	3	3
Performance	4	4
Security	1	1
Total	104	104

Lint increased!

[mahibi]

not to be merged for 20.1.0, might review only afterwards