After creating a new gist invalidate the cache and reload the list

If the *gists* buffer is present, reload the list without switching to
it. Otherwise, just invalidate the cache.

Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Merge commit '68d3a8a'
make background arg optional
leverage gh-profile

use of multiple accounts (for example with Github Enterprise) is
now possible.