[Refactor] Switch to QRegularExpression from QRegExp

I left in debug cruft for nifexpr because it's important that it's easy
to validate it against the old code.
[Refactor] Selectively flush textures for large speed up

Most of the settings in the Options menus would send sigChanged() for
the Options class, which would flush the textures.  This made using a
lot of things that don't affect textures sluggish, like lighting and
background colors.
[GCC] Build Improvements for MinGW

Automatically copy the lib and icu DLLs for shared builds
[C++11] Make some QHashes const with initializer lists
[C++11] `foreach` to `for`, const/const& where possible

Qt foreach macro is unnecessary in most cases with C++11's new
range-based for loop syntax.  **However**, foreach makes a copy and for
does not, and for cannot change something it is looping over.  I left
foreach loops in some places.

I also moved to const and const reference where possible, which are good
optimizations.
[C++11] Use initializer lists and uniform init where possible
[C++11] Much better syntax for signal/slots (part 1)

Got the biggest files so far.  There will be a few more chunks of them
to do.  The C++11 syntax Qt has for signals/slots is so much better and
more readable.
[C++11] New signal/slot syntax part 2
[C++11] Replace NULL/0 with `nullptr`
[C++11] Some fixes for GCC

I removed the "symmetric" disconnects also because it actually seemed to
break the connections.  I am still not sure if one disconnect() is
working either.
[C++11] Replace more NULL with `nullptr`

Apparently my search results were messed up when I searched for all
instances of NULL... :)
[C++11] More 0s to `nullptr`