[Fix] Read 'AppDir' path from recipe file.

[cabiste-dev]

Currently this tool only searches for the AppDir in the current working directory (unless --appdir is used) and completely ignores the path defined in the recipe file.

This PR fixes that.

The hirearchy of importance is:

1. --appdir (if used)
2. recipe.AppDir.path (if found)
3. defaults to searching for AppDir in the current working directory

[cabiste-dev]

Also please merge #316 asap

[cabiste-dev]

I'm kinda new to python, so can someone explain to me why the path concatination is done like this?

self.default_runtime_path = self.appdir_path / "runtime" / "default"
self.compat_runtime_path = self.appdir_path / "runtime" / "compat"

instead of using os.path.join() or converting self.appdir_path to a string then concatenating it with + ?