Implement batch action for inviting users to groups

[JammingBen]

Works towards https://github.com/owncloud/enterprise/issues/2865

[JammingBen]

This one is ready for review, sorry for not marking earlier. It needs #521 to be finished and merged first though, otherwise we permanently have merge conflicts with each force push to #521

[phil-davis]

I put this into the Classic Server Team Board project, and mentioned some people for review.

1 JS test failed - I have no idea if that is a real fail.

There is a conflict reported, so that n eeds to be sorted out.

[jvillafanez]

it might be better to use a set instead of an array. The operation should be more clear too:

var s = new Set()
s.add(user)  // guarantees uniqueness

[JammingBen]

I tried it, unfortunately Sets do not support uniqueness with objects.

[jvillafanez]

same as above, it seems better to use a set instead of an array

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
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[jnweiger]

Confirmed implemented in 0.7.0-rc.1