Allows for bluetooth to be turned on from TeclaPrefs. This can be done when "Connect to Tecla Shield" is pressed when bluetooth is off. 'no history' removed from manifest.

Fixed #148
Merge pull request #149 from k22mak/develop

Allows for bluetooth to be turned on from TeclaPrefs.
Handle null mode in KeyboardSwitcher
Merge branch 'develop' of github.com:idrc/TeclaAccess into issue-126