plainbox:impl:unit:job.py: Remove deprecated partial_category_id
plainbox:impl:exporter:xlsx.py: Fix job plugin filtering code

avoid using uneeded re.search()
plainbox:impl:exporter:xlsx.py: Add category support provided by units

VS categories provided by local jobs (the default mode).
Both are mutually exclusive.
To enable units categories, use the following exporter format option:
"with-unit-categories".
checkbox-touch:main.qml: Export to xlsx using the units categories

As opposed to categories artificially created using local jobs.
"automatic merge of lp:~sylvain-pineau/checkbox/xlsx_exporter_fixes/ by tarmac [r=zkrynicki][bug=][author=sylvain-pineau]"