obsplus.utils.events.strip_events will get recursion error on bad input type

[shawnboltz]

This is an easy fix, but I don't have time to do it right this moment so I just wanted to make a note.

Description
Inputting something other than an obspy Catalog or Event to obsplus.utils.events.strip_events with raise a recursion depth error due to inadequate type checking.

To Reproduce
Pass anything to obsplus.utils.events.strip_events other than a Catalog or Event object.

Expected behavior
Should raise a TypeError instead.

Versions (please complete the following information):
Affects all versions.