Expose main window object to javascript

Add a new magic C++ interface object, application, to the javascript
root context which controls the main window.
Merge branch 'develop' of github.com:BitShares/qt_wallet into develop
Add MainWindow::hideWindow

It hides the window.
Merge branch 'develop' into btsx
Merge pull request #16 from vikramrajkumar/btsx

Merge upstream