Implemented login to 9gag

First step on our way to like/dislike buttons is to be logged in.
Adding ability to like/dislike

- New class VotingManager, handles comms to 9gag
- New params in gagobject/gagmodel
- New settings for username
- New gui for login/logout
Fix login and voting

* Move login codes from NetworkManager to GagBookManager
* Remove reimplemention of cookiesForUrl and setCookiesFromUrl in GagCookieJar
* Remove manually save cookies after login - those are automatically done by QNetworkAccessManager
* Fix VotingManager creating another instance of NetworkManager - it should use the NetworkManager instance provided by GagBookManager
Remove saving of username to QSettings
Improvement to login/voting UI

* add busy property to GagBookManager and VotingManager
* show message when login success, login failure and voting failure
* GagObject isLiked and isDisliked properties replace by likes property
Port login and voting UI for Harmattan and Symbian
Improve LoginDialog
Merge branch 'login+voting'