Use the new packaging directory for MacOSX specific files, and provide shell script...

Use the new packaging directory for MacOSX specific files, and provide shell script workaround to make the svg icon reachable.

- Make use of the new packaging directory.
- Set a current directory for subsurface to find the svg icon.  There might be a pretter solution to this.
- Somehow subsurface doesn't behave properly in the Dock.  Running it in the background without Dock integration until we figure out why.

Signed-Off-By: Henrik Brautaset Aronsen <subsurface@henrik.synth.no>