Check trakt account details before saving user credentials

Uses new function 'TraktTV.checkDetails(user,shapass)' to verify with
trakt.tv if the account user/pass is valid, if yes, returns success else
failure. On error, displays error on page.
Function to check user credentials with trakt,

Simple HTTP post and return result
Added TraktTV credential alert and misc changes

Added alert that displays when trakt.tv returns an error when validating
credentials
Disabled User/Pass fields and Encrypt button while credentials are
already saved as they cannot be changed until credentials have been
cleared.