Simplify build instructions (#766)

Clean source directory (#765)

Clean source directory (#765)

Put Windows-specific stuff into win directory (#764)

Remove XCode files (#763)

Building process is abstracted by CMake

Only allow one of the data types (#753)

On Linux I encountered the bug that a file path was treated both as
file path data object and as text object.

Set minimum mac OS deployment target on Mac CI (#762)

Create universal binaries on Mac CI (#761)

Use TreeSheets as target identifier (#760)

The application name on Mac OS is determined by the directory name, i.e.
TreeSheets.app which in CMake is determined by the target identifier.

Fix Plist issues (#759)

* Prepare Plist on Mac CI

* Fix Plist

* Add file association and other attributes