Added new contextual option in account list to allow the user modify the password
AuthenticatorActivity is started when 'change password' is selected for a list in the list of accounts
Removed toast message for updating credentials when user manually accessed to the AcountAuthenticatorActivity
Fixed focus in AuthenticarActivity for changing password so that server URL is not editable
Make the 'refresh' button enabled when visible, although the URL-input field is disabled, when the password is being updated
Updated some messages in login activity