Don't attempt to stash new section edits

The parser output of edits produced via the 'new section' interface varies on
both the edit body and the edit summary (since it determines the new section's
name). So there isn't an early point in the edit process where we can start
computing the edit output. We have to wait for the user to be completely
done, by which point edit-stashing provides no advantage.

Change-Id: Ida461e08189b75c5a508628d11dc929a6138814a
(cherry picked from commit c4f67e5a3a8c3286487ad10b575730c9b0204b0a)
Make ApiStashEdit use the StashEdit log group, rather than PreparedEdit

An early version of what ultimately became commit 3a6c9d36c used
'ApiPreparedEdit' instead of 'ApiStashEdit'. The class / file were renamed but
not the log group.

Change-Id: Ib4de1f1f21f058d3be627048bc93e7730515d340
(cherry picked from commit afd317ac50878f750fccecc3fb4064c350991e34)
Merge "Make ApiStashEdit use the StashEdit log group, rather than PreparedEdit" into wmf/1.25wmf11