A few keyboard shortcut improvements on Explore page

[misaugstad]

A few things I've noticed while testing are that

1. If the user is holding ctrl, we should be ignoring keyboard input (refreshing with ctrl-R shouldn't add a tag, trying to copy with ctrl-C shouldn't switch you to curb ramp labeling mode)
2. Hitting the esc key should take the user out of "labeling mode"

Neither of these are a common problem, I mostly run into them when I'm doing a lot of stress testing.