Disable reverse search, restore "?" for help popup.
Map Ctrl+F to searching in CodeMirror, map Space to PageDown.
Take Ctrl+A back from Vim mode for selecting all text.
Disable Ctrl+O in Vim keymap since it's used by some browsers.
Add explanation of key commands to help popup.
'/' still starts a CodeMirror search instead of a Gerrit one.
Jumping within Gerrit using the 'g' prefix is still not supported.
Change-Id: Id77faa4b36add35c78edfd0d7d0611279cbe7120
6a45079cb6