Can't clear tab responses

We should be able to clear out query/mutation responses. `Cmd-k` like in the shell should be a convenient shortcut for this, as well as a button in the response section to clear it out.

Note: reloading the page seems to work for the first tab, but _only_ the first tab. I have a 7 tabs open to conveniently manage all my different queries and i can't seem to clear those responses out.