Qt support

Initial version (call it alpha) of support for Qt platform.

#### What does work:

* Main page
* Search
* Language selection
* Settings (application live-time only, no storage enabled yet)

#### What doesn't work:

* Always on-screen top and bottom toolbars. I moved bottom toolbar to top (because of qt webview limitations)
* Auto complete search input
* Bookmarks
* Maybe something else that I'm not aware about