Move "Compiling on MacOSX" documentation from Wiki to Git

• Move the contents from the Wiki page https://wiki.inkscape.org/wiki/CompilingMacOsX to Git
• Remove short-lived or outdated contents
• Cleanup

Please note that I do not have MacOS, therefore review by someone with more knowledge is neeeded.

• There are some open questions that I added as TODO comments. These need to be answered by someone who knows MacOS. --> worked around in the text