Improved login form usability.

Added an automatic navigation from username to password field.
Added a login action once the user submits a password.
This makes login form easier and faster to use.
Merge branch 'master' into improve_login_form_usability
Merge pull request #5 from mdzyuba/improve_login_form_usability

Improved login form usability
Merge branch 'master' of https://github.com/openMF/android-client