Visual C++ 12 fixes/workarounds.

- Removed copy ctor and assignment operator in Renderer to workaround Visual C++'s move behaviour.
- Got rid of VC12 conversion warning.
- Removed preprocessor condition in Signal.hpp by dropping copy ctor and assignment operator. Provided custom move ctor and move assignment operator for satisfying MSVC who does not like =default.
Adjusted CMake config file.

- Removed unrelated configuration options (SFML options).
- Reduced amount of branches (simplified).
- Less cache overwrites/hacks.
- Unobtrusive compiler flags.
- Removed LIBRARY_OUTPUT_PATH.
Removed copyright line, fixed doc install target, added configured version.
Updated changelog.