RE-ENABLED PROVING_GROUNDS && FIXED SCRIPT ERROR FOR ALL CLIENTS

- the initial script error does not show up anymore; certain builtin functions were removed from A3 coming from A2 which were still called; hence the error
- there still remain some script errors within the proving_ground addon but those are a) only shown to clients that have access and b) seem to have no impact on actual functionality of the addon; I propose to completely replace the current proving_grounds with a newer version somewhere down the line