It's actually quite hard to build a front-end for fwupd at the moment
as you're never sure when the progress bar is going to zip back to 0%
and start all over again. Some plugins go 0..100% for write, others
go 0..100% for erase, then again for write, then *again* for verify.
By creating a helper object we can easily split up the progress of the
specific task, e.g. write_firmware().
We can encode at the plugin level "the erase takes 50% of the time, the
write takes 40% and the read takes 10%". This means we can have a
progressbar which goes up just once at a consistent speed.
More than one person has asked about 'why call fu_plugin_update() for a
reinstall or downgrade' and I didn't have a very good answer.
The plugin API is not officially stable, and we should fix things to be
less confusing. Use the same verbs as the FuDevice vfuncs instead.
