Restricted collaborations

[deivid-rodriguez]

:tophat: What? Why?

In this PR I add a feature action "support" and a couple of feature hooks:

• One adds our default authorization by default to all feature instances created.
• The other one makes sure that the minimum feature conditions are kept when updating feature permissions.

Note that in the case of the permission update being invalid, I'm just rising. I think that's enough for now until we add a proper form with proper validations.

Finaly, I using the new "support" action to properly authorize the links and conditionals in the collaboration template. This logic is quite complicated, not sure if my changes are correct or what we want. I you want I can extract those changes to a separate PR so they can be discussed separately?

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[deivid-rodriguez]

Updated to point to latest decidim master now that the related PR in decidim's master has been merged!