Call Build service to test if project is executable

[ZdenekM]

https://github.com/robofit/arcor2/blob/e35859580cd3100cbfaa6b7cab9f1a921779875b/src/python/arcor2_arserver/rpc/project.py#L221

...the same should probably happen after a project is saved and based on the check, the "Build package" / "Run project" button in the AREditor should be set enabled/disabled.