PR3296 auto export (DRAFT)

[vanelsberg]

This PR#3451 enables automated settings export. As settings export needs the master password for encryption the password is stored on the local phone's app datastore on manually exporting settings from the maintenance menu. Password will expire/wipe when not used for the number of days set. Stored password wil be wiped on settings master password (or forced with file 'ExportPasswordReset' in /AAPS/extra)

Functionality is enabled through a new setting in Maintenance preferences. Once enabled (and password set through manual export) user can define the automatic settings export from automation.

Actions also wil be in registered to "Treatments" (careportal/User entry)

TODO: Review/determine if storing the master password unencrypted local phone's app storage is acceptable. See also issue https://github.com/nightscout/AndroidAPS/issues/3296

Additional note: This PR implementation should enable implementation for auto exporting to alternate storage locations (like the Downloads folder or Cloud). But this will be subject for another PR.