Remove collaborative from Core

This PR is opened for testing Codiad without collaborative included.

The collaborative plugin can currently be triggered from https://github.com/daeks/Codiad-Collab and the marketplace. 
There should be no need to delete /data/collaborative/ folder

Warning: This PR is currently not going to be merged as the plugin is missing in the market.

ref. to https://github.com/Codiad/Codiad/issues/536