It seems a little odd to call it 'Update' when it's being used for downgrading
and reinstalling as well.
As we're making things simpler, just use a single 'install' action in fwupdmgr
rather than 'install', 'update-online', 'update-offline'. We can use the flags
and fallbacks to do the right thing in all cases, and make the typical case
(installing a local file to any matching hardware) simple.
Fixes half of https://github.com/hughsie/fwupd/pull/23
