[Feature] (App): Search for PRs

[dacharyc]

Is your feature request related to a problem? Please describe.
Sometimes, I know I saw some word or phrase - a PR related to a specific new feature, for example - but I'm not sure which list or dashboard it's currently in.

Describe the solution you'd like
I'd like to be able to search for a keyword or phrase and view PRs whose title, description, and maybe comments/reviews/commits refer to that keyword or phrase.

It might also be nice to be able to specify what to search - i.e. search a title for this phrase, search comments or reviews, etc. i.e. "I know I saw this in a comment somewhere..."