Reset state to idle when space inserted

Fixes #2.  If a space is inserted, it must have been the first letter
typed, otherwise the menu would have come up.  We never want to look up
these spaces -- we know what they're for.  Just do the hiragana
insertion, then reset kanji startpoint and set state back to idle, ready
for the next input.
Activate vimes before motion-driven kanji conversion

Doing this means all the vimes keymappings, etc will be activated.
We have to disable the insert mode mapping on our way in, as we are
setting the value of g:kanji_start_point outside of insert mode and we
don't want it to be reset, however it needs to be re-enabled once we're
in, in case the user leaves insert mode without de-activating vimes.
WIP -- drop select box on esc
WIP fix for #5