Fix facet bug on PyQt4

Add tests

Closes #335
Always draw show help
Change pip command
Merge pull request #345 from ChrisBeaumont/335

Fix facet bug
Merge pull request #346 from ChrisBeaumont/showhelp

Always render drag data helper
Interpolation=nearest in PV slices
Slice documentation
Update mri image
Merge pull request #348 from ChrisBeaumont/pv_doc

PV Documentation
Update vimeo iframe
Plotly and categorical data improvements
update plotly tests for API change
Merge pull request #356 from ChrisBeaumont/category

Categorical data enhancements
Fix swap_axes under PyQT

Closes #349
Merge pull request #357 from ChrisBeaumont/swap_axes

Fix swap_axes under PyQT
Fix log ticking bug

Closes #354
Subset styles stay synced after restoring

Closes #352
Relabel cid->label in Data.add_component_link

Closes #351
Data.add_component accepts ComponentLinks

Closes #350
Merge pull request #358 from ChrisBeaumont/bugfixes

Various bugfixes