Remove onlyShowUnchanged

Closes #1011 
The idea of onlyShowUnchanged seems to be that we needed to essentially filter the integers from the non-integers.  Consider the domain [0,2].  The defaultTicks that would show up would be [0, 0.5, 1, 1.5, 2], but let's say that they only want the integers.  Previous they would set the onlyShowUnchanged to true and this would be done from the formatters in a pretty clunky fashion, but instead this integerTickGenerator can/should be used.

If you can think of other generators that were previously worked around via onlyShowUnchanged, we might want to add that to this.