NEW/BREAKING: refactor CMake-Code, so static/dynamic switch is done via <code>BUILD_SHARED_LIBS</code>, which retires <code>JKQtPlotter_BUILD_STATIC_LIBS</code>, <code>JKQtPlotter_BUILD_SHARED_LIBS</code> and removes the capability to build static and shared libraries in one location (fixes issue #104)
NEW: prepareed library for CMake's <a href="https://cmake.org/cmake/help/latest/module/FetchContent.html">FetchContent</a>-API
NEW: the different sub-libraries JKQTPlotter, JKQTFastPlotter (DEPRECATED), JKQTMath, JKQTMathText can be activated/deactivated with CMake options JKQtPlotter_BUILD_LIB_JKQTPLOTTER, JKQtPlotter_BUILD_LIB_JKQTFASTPLOTTER, JKQtPlotter_BUILD_LIB_JKQTMATHTEXT, JKQtPlotter_BUILD_LIB_JKQTMATH
- removed more global settings (these are now target-specific)
- exporting now Config.cmake, which contains find_package(Qt) and loads a separate Targets.cmake
Previously it could not find the cmake file and giving an error:
```
CMake Error at CMakeLists.txt:15 (include):
include could not find load file:
JKQtPlotter_LIB_properties
```
- enabled compiler-warnings in CMake-build
- several bugfixes (also to appveyor.yml)
- removed some function from JKQTBasePlotter, which were (messy) shortcuts to adding graphs
