Remove/update old calls to Meteor.flush()

[edemaine]

Fix #235. Some calls to Meteor.flush() (in events) seemed unnecessary, while other calls to Meteor.flush() were actually needed (to upgrade the web UI according to session variables before trying to modify the contents) and replaced with Tracker.flush(). Now no errors in my app.

I've gone ahead and published my own fork which incorporates this PR as well as @TechplexEngineer's fixes. You can use it via meteor add edemaine:accounts-ui-bootstrap-3.