Wrapped helper and template methods with try-catch to prevent exceptions from breaking the whole Meteor app

Re-do of PR #1487 that got broken somehow. Original comment below:

A small bug (like a null dereference) in a helper or template method can break a whole Meteor app (causes a blank screen). Wrapping calls to these methods with try-catch and not allowing exceptions to bubble-up is a good solution.

Please see detailed explanation at https://groups.google.com/forum/#!topic/meteor-talk/O0B6lA-hSUE