GitLab

- display the list of user's instance trees
- display the instance trees's connection parameters
- allow instance tree's parameters modification
- request new instance

Reuse as much as possible the code from https://panel.rapid.space.
Fetch all dependencies with a Makefile to simplify code updates.
Do not use rapid space's icon.

Try to load the software release json schema from slapproxy public directory,
as this UI will be used on offline servers.