Allow specifying different sync conditions per folder (fixes #57)

[Catfriend1]

Purpose
Provide the ability to specify different sync conditions for each syncthing folder through the wrapper UI.
Available conditions per folder:

• Sync on WiFi
• Sync on specified WiFi
• Sync on metered WiFi
• Sync on mobile data

Screenshots

Related issue:
#57 "[FR] Feature Request: Different synchronization conditions per folder"
syncthing/syncthing-android#511
syncthing/syncthing-android#1186
syncthing/syncthing-android#1225

Related bounty
https://www.bountysource.com/issues/28940393-enhancement-request-per-folder-sync-only-when-charging-on-wifi

Testing
Verified working at commit 5f005c5 on:

• AVD Android 9.x
• Xiaomi Mi8 running MIUI 10, Android 8.1.0

[Catfriend1]

Uhh this is a lot of work, but it grows fine :)

[Catfriend1]

@Review/Complete.
lgtm.

[Catfriend1]

@oneyb
The feature you requested in syncthing/syncthing-android#1186 is now implemented in Syncthing-Fork.

[Catfriend1]

@JohnCardenas @sim6 @amette @Flowdalic @hvhaugwitz @edgimar @robert7k @Aq32 @mrbrahman
The feature you requested in syncthing#511 is now implemented in Syncthing-Fork.

[Catfriend1]

@karlicoss This is already released with Syncthing-Fork. Bounty's welcome :) @68516-karlicoss

[karlicoss]

@Catfriend1 awesome, didn't realize this fork existed. Just seamlessly switched from the original app so thanks :)
One small question -- if I want to keep folders A, B and C synced on wifi and folder D on mobile network as well -- is the quickest way enabling mobile sync globally and adjusting per-folder sync for A, B and C to disable mobile sync? If I do it the other way around, that is, disable mobile sync globally, and try to enable it for D only, it doesn't work as mobile sync seems to be grayed out in D sync settings.
Also a GUI suggestion: might be nice to display sync settings summary perhaps as small icons in 'Folders' tab. But that's a really minor thing so probably only worth for someone really keen on polishing the UI to implement.

[Catfriend1]

@karlicoss

is the quickest way enabling mobile sync globally and adjusting per-folder sync for A, B and C to disable mobile sync?

Yes. I intend to improve this by "whitelist-thinking" in issue #110 but currently I'm focusing on other improvements. This "positive way of thinking what a user enables" instead of the "negative" disabling would be easier but turned out to be a lot of work on the code and requiring intensive testing before release.