workarounds for issue #194

This has two workarounds for issue #194 - removing the filter hint (called 'info_text' in FilterBox)
and not showing the assignments in the machineslist that the machinechooser uses.

I added a show_assignments flag to machineslist, and we can probably leave that in once the workaounds are no longer needed.
As such I only labeled the one line that actually sets that flag to True as a workaround.
pep8 fixes
Merge pull request #195 from Ubuntu-Solutions-Engineering/placement_ui_hacks

workarounds for issue #194