Define Histogram color cycle

[philippjfr]

As suggested in #918, bokeh Histograms should have the same color cycle as the matplotlib version defined.

Before the PR:

With the PR:

[philippjfr]

Would you look at that Travis reporting the exact change in the bokeh data:

{'values_changed': {u"root['roots']['references'][38]['attributes']['fill_color']['value']": {'new_value': u'#036564', 'old_value': u'#30a2da'}}

Tests will have to be updated.

[jlstevens]

Looks good and I am happy to merge once the tests are updated and passing.

[philippjfr]

Tests regenerated and push builds passed. Ready to merge.