Add HistorySearchUp and HistorySearchDown actions which are similar to
HistoryUp and HistoryDown but search for the prev/next history item
whose beginning matches the currently entered text in the infobuffer
(more precisely, the text before cursor).
Also fixed the following issue: if we scrolled to an older history item
and then edit the infobuffer, this older item gets modified.
We should not edit old history entries. So in this case set HistoryNum
to the last (newly added) item and modify the last item.
This commit exposes the separate infopane bindings to configuration
from the user. This also adds support for separate bindings in the
terminal emulator view. Default bindings are provided, but can also
be rebound in bindings.json.
This commit separates actions in the command bar from actions in
a normal buffer, and implements what is needed to allow rebinding,
although an interface for command bar keybindings is not yet exposed
to the user.
