Change 'all contributions' checkbox in the webcast/recording request form

When selecting the contributions for a webcast/recording request, there is an 'All contributions' checkbox, but it is not flexible enough:

* User might want to check all but a few contributions in a huge list.
* User might want to record virtual contributions (or held in a room with no video-conference equipment)

One solution could be changing it into a button that checks/unchecks all the contributions.

Start from the webcast/recording request form and inspect how the contribution-selection checkbox handles the list. The change is complete when users can select or clear all contributions, exclude individual entries from a large list, and include virtual contributions or room-only contributions.

Written by the indexing model from the issue text.