Remove unused or unnecessary code

[Krakonos]

There is a lot of code that isn't necessary, or even not used. Let this be a tracker issue of what I know of:

• [ ] macos/ Some legacy scripts, might yet be useful for localization
• [x] windows/ Old installer files. I'm not aware of any value in them, could be removed.
• [x] mobilemerk/ Presumably read-only version for mobile devices. I think it's not worth pursuing this vision when we have so many mobile mapping apps. Could be removed at any time.
• [x] translations/*.qm These files should be generated from ts when required. Could be removed at any time.
• [x] 3rdparty/quazip* There is a package for Mac (homebrew), Win (MSYS) and most Linux distribution (Debian, Ubuntu, Gentoo, Arch,..). Could be removed at any time, but a bit of testing is in order.
• [ ] 3rdparty/qtsingleapplication It's used to activate already running instance. It's an old piece of code and I'm expecting some future version of Qt will break it. A good replacement is required.
• [ ] src/QMapControl/ Some of the files there are not used, and the whole thing could probably be consolidated into something much more transparent
• [x] src/Backend/Spatialite* Does not even compile and I really don't want to work with sqlite/spatialite anyway, as they are way too touchy for my taste.

I don't know of anything else. Feel free to suggest more stuff, or convince me some of the above is worth keeping around. I will start the cleanup after 0.18.3 release.

[a17r]

What about qrcode/zbar? Upstream seems pretty much dead and merkaartor depends on zbar-qt4 headers.