Detect edits which don't actually change projects in Maniphest tasks

Summary:
Be smarter about detecting when projects haven't actually changed so we don't
create silly transactions which just reorder them or change (entirely arbitrary)
dictionary keys.

Test Plan:
Edited a task with several projects and swapped their order, didn't get a bogus
project transaction.

Reviewed By: tuomaspelkonen
Reviewers: tuomaspelkonen, jungejason, aran
CC: anjali, sandra, aran, tuomaspelkonen, epriestley
Differential Revision: 249