Keppel: delete multiple repositories at once

[majewsky]

I have a customer (@stephanzlatarev) who often needs to delete several repositories at once. He finds that deleting each repository individually is quite inconvenient, especially when you take #967 into account as well.

There should be either some kind of multi-select mechanism where multiple repositories can be selected and then deleted at once. Or, as a slightly simpler alternative, there should be an action to delete all repositories currently on screen. In the aforementioned customer usecase, the customer could use a filter string to restrict the repo list to those that he wants deleted.

In any case, there should be a confirmation dialog listing the names of all repos that get deleted and how many images are in them.

[majewsky]

Still relevant. (Note that #760 is related, as being the same question, but about images instead of repos.)