hijack nextbutton on preview page and rename it to Submit!
Summary:
it's very awkward when you don't know when a change happens or
not, so suitably label the next button so it actually says submit when
it will trigger the report submission.
CHANGELOG: Buttons are more suitably labled when bug reports are submitted
Test Plan: file bug report -> preview page has submit button -> going back it is not submit -> clicking submit it also turns back to next (albeit disabled)
Reviewers: Plasma, VDG, ngraham
Reviewed By: VDG, ngraham
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D22289