Add additional app and clipboard timeout options

[numericOverflow]

Added more timeout options to give user more flexibility to choose their timeout. These apply to both the app_timeout_key and clipboard_timeout_key.
New values: 15m,30m,60m,90m,2h,4h,6h,12h,24h

[numericOverflow]

This commit will close issues #488 and #352

[bpellin]

I don't think adding more time to the application timeout will help much in practice. The application will frequently be closed by Android to free memory before we hit the longer limits. I think we first need to put in place the ability to automatically reload the database from the file after the application is closed.

[numericOverflow]

No worries. Thanks for all the hard work, but I've moved on and now use Keepass2Android ( https://play.google.com/store/apps/details?id=keepass2android.keepass2android ) which I prefer over this app.

[pfn]

Add a low priority foreground notification (with a foreground service) This will prevent android from closing the application.

You can apply this to the copy to clipboard notification or create one after opening the database