[2.11..2.13] Fix showing the local inactive profile in json mode
When aa-genprof proposes a local inactive profile, it had a hardcoded call to 'less' to display that profile.
Unsurprisingly, this doesn't work in JSON mode and breaks YaST (luckily it's only a case of "the button doesn't work").
References: https://bugzilla.opensuse.org/show_bug.cgi?id=1171315
As groundwork, split off UI_ShowFile() from UI_Changes. UI_ShowFile() is more generic and can be used to display various (text) files, not only diffs.
This was fixed in master in !514 (merged), but cherry-picking failed because of whitespace diffs in ui.py.
I propose this MR as backport to 2.11..2.13