[macOS] Allow the app to be run from $HOME/Applications

Currently, Drive is allowed to be run from the /Applications folder only.
But there is also a user application folder: $HOME/Applications.

The user folder would be a better location by default, but it is not doable (DMG cannot be told to create the folder if it does not exist; and creating a .pkg installer is too complex and has no value yet).

This new folder is a good idea for:

• Users having no rights into /Applications.
• Testing the auto-updater on our agents that do not have such rights.

So, after a lot of testing and POCs, what can be acheived is to allow the app to be run from the user folder and "/Applications".

The FinderSync extension will work in both folders.

Finally, real changes will be:

• To update tools/scripts/check_update_process.py to use the user folder.
• To make the FinderSync extension location agnostic.
• To make the auto-updater location agnostic.

It will not change default behaviors, so no regressions are expected.