Ability to select multiple rounds to filter on in all submissions view

[wes-otf]

Right now the filtering menu only allows a user to filter on one round, while manually using query params ie. ?round=123&round=456 is recognized by both the filtering table and the menu.

[frjo]

We guessed that only single rounds was ever filtered for so made the UI for that. Should be easy to change to a multi select. More filters you want this change for?

[frjo]

Reviewers filters are already multi select but most others are single select (Fund/Round/Status etc.)