IE8 viewport code: Use a global event instead of a listener entity

The advantage of this approach is: IE8 code has the same number of
entities as other browsers, so Crafty('*') behaves predictably etc.
Also, this change removes a layer of unnecessary abstraction /
complexity.
Merge pull request #558 from sbyrnes321/viewport

IE8 viewport code: Use a global event instead of a listener entity
fix unit-tests to avoid false-positives in IE8
Merge pull request #559 from sbyrnes321/IE8tests_take2

fix unit-tests to avoid false-positives in IE8