Implement Backup/Restore

[yvolk]

Backup/Restore should be implemented according to this documentation: http://developer.android.com/guide/topics/data/backup.html

1. Databases, preferences (in files) and Accounts should be backed up.
2. Maybe Avatars should be (optionally) backed up also?! They may be really needed for older messages, for which these avatars may be not available online now.
3. In addition, I guess we should encrypt passwords/tokens, using e.g. password, provided by a user during backup/restore (if this is possible...)

Current state of implementation as of 2020-04-27:

• The feature is located in AndStatus Settings -> Storage -> Backup.
• Points 1 and 2 above implemented. I.e. attachments and avatars can be optionally backed up and restored (just set "Backup media files" checkbox)
• Log files can be backed up and restored also. Just set "Troubleshooting -> Backup log files" checkbox.

[yvolk]

The basic implementation of this feature is done in current commit. Not released yet.
There is an automated test for this, which passes, ( see https://github.com/andstatus/andstatus/tree/master/tests/src/org/andstatus/app/backup ) but I didn't have a chance to test it using a real Android Backup Manager (see http://developer.android.com/guide/topics/data/backup.html ).

Please test the implementation!

[yvolk]

Interactive, manual backup and restore implemented. The interface gives clear view on the progress and the result (success or failure). See the screenshot

[yvolk]

Released in AndStatus v.9.0
I found this feature very convenient to clone my AndStatus configurations and data between my devices.
Plus, now it's very easy to test new versions without risk of losing all accounts and messages.
I was pleased to see that my whole database with 57000 of cached messages works quite well on Nexus One :-)