Run Chrome incognito in split mode

Since we now have a LRU cache, be very paranoid about the
incognito <-> normal browsing boundary. This runs the extension
in a separate process in incognito mode (no shared cache, etc.)

Signed-off-by: Nick Semenkovich <semenko@alum.mit.edu>
Merge pull request #165 from semenko/incognito-split

Run Chrome incognito in split mode