Fixes for bokeh 0.12 compatibility #725
As the title says this PR makes HoloViews compatible with the upcoming bokeh 0.12 release. Since bokeh is going through rapid development cycles and we do not want to accumulate endless compatibility layers we are also dropping compatibility with 0.10 in this PR. The major component of this PR is in changing the way JSON patches are computed when using the widgets and callbacks, which has now been unified to use the same approach everywhere, bypassing the relatively slow patch diffing that bokeh uses by default and also dropping various hacks previously added to make things work across 0.10 and 0.11. This PR also does not yet add support for any of the new features in bokeh 0.12. Those should follow in future PRs; for now this PR just makes sure all existing functionality continues to work.