[ci skip] start implementing Facebook SSO

add controller 'SigninFacebookCtrl', factory 'Facebook'
change the name of method which signs the user in with Dash account into 'signInDash'
change controller 'MainCtrl' to check if the user has signed in so that the user who has signed in can be redirected to dashboard
add 'getUserId()', 'updateUserInfo()', 'checkSignIn()' methods for the factory 'Account'
add string resources for Facebook SSO
add style definitions for Facebook Login UI
update 'main' view to support Facebook Login