Split repo generation functionality out of blenderpack.py

Moved repo.json generation to make_repo.py
Package/addon parsing is getting a bit messy, this can be
cleaned up when we have a clearer idea of what a package is.

For now just make it work.

utils.py

@@ -0,0 +1,6 @@
+from pathlib import Path
+import json
+
+def dump_repo(repo_path: Path, repo_data: dict):
+    with (repo_path / 'repo.json').open('w', encoding='utf-8') as repo_file:
+        json.dump(repo_data, repo_file, indent=4, sort_keys=True)