Qt 5 Port

### Overview 
Qt 5 Port - Closes #28
NifSkope.pro file cleanup - Closes #27
Project Restructure - Closes #31
FSEngine Refactor - Closes #36
Dev- and Linux-specific code - Closes #38

<sup>_(Hopefully I [got the syntax right](https://github.com/blog/1506-closing-issues-via-pull-requests))_</sup>

Only thing I can think of to bring up for discussion is the inclusion of `/build/doxygen/tags` folder (0ae1f9f6492f96ed538835ee29addbda781ab814), which includes tag files for Qt 5, which is just a long list of classes/class members in an XML file in order to make the the NifSkope API documentation much easier for developers to browse.

I'll provide [NifTreeView as an example](https://dl.dropboxusercontent.com/u/9491126/apidocs/html/class_nif_tree_view.html), since the main NifSkope class has a scary collaboration diagram.   You can browse the other docs if you want, but notice that anything with a Q* is clickable in the inheritance/collaboration, and also in all the member descriptions, and sends you to the official documentation.   Furthermore what I love is it lists all the [inherited member functions](https://dl.dropboxusercontent.com/u/9491126/apidocs/html/class_nif_tree_view.html#pro-methods).  

So, ignoring the fact that it's ~11MB I think it's very useful.   I guess that I could also put them into a 7z which is ~350KB... and then have my doxygen make target decompress the archive before running doxygen.  But I didn't think of it until now... :)