Catching a few more process events.

Installation still not very smooth. Seems you have to manually paste in
whatever unique ID Chrome assigns when loading the unpacked extension into
the allow_origins of host/org.vim.stayfresh.json. The most reliable process
I have found is:
- Load the unpacked extension.
- Copy the ID from the chrome://extensions page (make sure "Developer mode"
  checkbox is checked)
- Add that ID to the allow_origins list in org.vim.stayfresh.json along with
  the others. Seems that wildcards are not allowed.
- Run ./INSTALL again to re-copy the host manifest file to the right place.
- Restart Chrome
- Possibly re-load the extension? Not sure if this is necessary.

If the extension is distributed through the Chrome web store then the ID
will at least remain constant. But then it's an awkward situation where user
has to download extension from the webstore, git-clone this repo, and then
run the INSTALL script just to copy the manifest file to the right place.