Support extras for ACTION_VIEW + mailto: URI

Support the extras documented for ACTION_SEND to be used with
ACTION_VIEW to support another app that doesn't care, namely Twitter.
Alternative fix for issue 5697 - ASUS display bug
Don't crash when startActivity() fails

Fixes issue 6201
Change message body font size with slider, using new setTextZoom() WebView API, from 40% to 250%
Fix display error in account settings

* correctly initialize summary of 'Server search limit'.
* don't persist value in shared preferences
Save/restore slider state
Merge pull request #448

Change message body font size with slider
Updated Japanese translation. catch up with 4955e34.
Updated Japanese translation of the changelog.
Should disable COMPOSE menu item

When message viewing and tap the next icon, menu icons (previous, next, delete and replys) disappears for an instant.
But a compose icon remains, then tap it accidentally.
Enable AOSP builds
Build with SDK 19
Add support for KitKat's Storage Access Framework

This allows users on KitKat to add multiple attachments at once.
Fix 'endless' loop in ImapFolderPusher

Under certain circumstances it's possible that the 'push state' isn't
updated to contain the most recent 'UIDNEXT' value. In that case
ImapFolderPusher.start() would execute the same code path through its
main loop over and over again, preventing the device from going to
sleep.
Rather than changing the code to update the 'push state' in the corner
case that triggers the behavior described above, this commit introduces
another mechanism to track the 'UIDNEXT' value. This should also catch
as of yet unknown cases where the 'push state' isn't properly updated.

At some point in the future I hope we get to a point where we only
persist the 'push state' when we manually stop/restart the service.
During normal operation there's no need to read from/write to storage
all the time.

Fixes issue 4907
Remove old setting for message content font size

- export new setting
- add upgrade code to convert old setting to new format
Update changelog for 4.901
Extract code to scale the slider value for the message content font setting
Bumped manifest to 4.901
Fix version codes in changelog
removed unread field mAccount