Improve OSX installation for mac

[BenoitBouillard]

Add an easy way to install and launch Course_Generator on mac with a standard installation package (.pkg).

Actually, the only way is to launch with a command line.

[patrovite]

Is it possible to create 'pkg' from linux? Like that I can generate a new release by myself. Otherwise I'll need your help each time I release a new version.

[BenoitBouillard]

I think there is 3 steps to do:

1. Create .app to launch the application easily. It could be done from linux
2. Signing the application to not having to deactivated gatekeeper. Seems not possible from linux
3. Create package for the deployment