use chooser for sendmail (remove explicit gmail) in LogHistory
allow user to save choice of app for sending log
warn user if no app for sending log available
integrating @davivels remarks
Fix. Avoid load logs again when changing device orientation
Merge branch 'fix_protocol_send_mail' into fix_logs_change_orientation
Merge pull request #781 from owncloud/fix_logs_change_orientation

User chooser for sending mail in LogHistory (with crash fixed if device is rotated in the e-mail app)