Irichter/fix 5294

This change fixes #5294.

The live development didn't work if the path for the `--user-data-dir` (passed to Chrome(-ium) command line didn't exist. Previously we constructed a path to /tmp/, but some users reported that this didn't work on their systems.
In order to fix this behavior, we now use the appSupportDirectory to store the user data directory.

The new place for the user-data-dir is now in `~/.config/Brackets/live-dev-profile`.
To find the place of the appSupportDirectory, the call to `gtk_init` had to be the first when the app starts to make sure that g_get_prgname() and g_get_config_dir() will return valid locations.