Push UI: Make it more obvious when the connection lists can be scrolled

[helen]

Is your enhancement related to a problem? Please describe.
Coming out of working on #589, I noticed that I got tripped up a few times not understanding that there were more results in the two lists (available connections and selected connections). I tried an interesting looking CSS shadow approach but it didn't work because of the individual item background colors.

Describe the solution you'd like
I am not entirely sure what the solution or solutions might be here, so we should definitely discuss in this issue. My initial idea is to add counts to the lists, likely just as parentheticals or something similarly not connected to other strings to keep localization issues to a minimum.

Designs
n/a at the moment

Describe alternatives you've considered
See above re: CSS shadows, also just... leaving it alone.