Edge Browser: Move Invite Assignment textbox to top of the column

[enrubio]

Right now the textbox for Invite Assignment shows at the bottom of the column. When there are a lot of reviewers it's easy to miss that it's even an option or enabled. Also, when you "load more reviewers" the column extends and it pushes the textbox further down. It'd be nice to keep it at the top so it's always visible.

[xkopenreview]

i think the idea is to use existing reviewers first
when you scroll to the bottom but still can't find any suitable reviewers
then invite outside reviewers