versionpage used KAssitantDialog's setAppropriate but that triggers
internal re-evaluation of button states as per the appropriateness of
adjacent pages of the current page.
this then would short circuit when a premature conclusion page was shown
(because the user provided no or insufficient information to file a
report) and result in the back button getting enabled even when that
wasn't reasonable (i.e. finished was emitted with showBack=false).

notably this broke for none-kde addresses that aren't routed into
bugzilla iff bugzilla responses are so slow that they'd arrive after the
user reached the conclusion page

the fix for this is super awkward. instead of using the existing
appropriateness system, use a higher level one on our end. this also
requires us to be able to iterate the page sequence. to achieve that we
now put all pages in a vector in the sequence that they are in the
pagedialog. on page changes we then establish whether we were moving
forward or backward and this way skip over inappropriate pages.

(could have used the hash, turn it into a map and use that instead, of a
new vector but honestly I want the hash to go away and we'll manage the
hand full of extra bytes until then)