Continue Modernizing Code / Warnings

There are some additional static-analysis cleanups that could be done to minimize warnings and improve the code. Some of these can be run easily from Qt Creator.

Please consider running one of the following, fix some things, and submit a pull request.

• Fix GCC / Clang warnings
• Cppcheck: https://github.com/danmar/cppcheck
• Clang static analyzers / clang-tidy: http://clang.llvm.org/extra/clang-tidy/
• Clazy (clang KDE/Qt checks): https://github.com/KDE/clazy
• Include-what-you-use: https://github.com/include-what-you-use/include-what-you-use