Redundant information in bug description files

[ChrisTimperley]

Various fields that appear in the reproduction-images section are duplicated by the bugzoo section (e.g., bug and fix commit).

[gavanderhoorn]

Note: the duplicated timestamps in fix.time and time-machine.datetime is on purpose (I would say since at least #270): the former captures the exact time a fix was committed, the latter the date & time the time-machine should use when generating the .rosinstall file.

There are many cases where these two are not identical, and being able to specify a different stamp than the date of the commit of the fix actually helps with reproducing bugs in unreleased repositories or packags (see #269).