[Localization] Add Greek translation qt_el.ts

[Oswald Buddenhagen]

On Sun, Dec 21, 2014 at 12:59:11PM +0100, Dimitrios Glentadakis wrote:
> I am one step before pushing my commit and i'd like to be sure for the 'git
> push' command.
> It is ok to use:
> git push ssh://codereview.qt-project.org/qt/qttranslations
> HEAD:refs/for/stable
> ?
> 
no literal "stable" branch exists any more. 5.4 is the current stable
branch.