Apostrophe 2.9.2 released: compatible with MongoDB 3.3+

[boutell]

• Starting with MongoDB 3.3.x (?), it is an error to pass safe: true when calling ensureIndex, and it has never done anything in any version. In our defense, this cargo-cult practice was probably adopted back in the days when MongoDB would invoke your write callback without actually confirming anything unless you passed safe: true, but apparently this was never a thing for indexes. Removed all the safe: true arguments from ensureIndex calls.
• Added a beforeAjax Apostrophe event to facilitate progress display and animations when using the new data-apos-ajax-content feature.