Merge pull request #198 from jzuhone/master

Enabling user-supplied matplotlib colormaps
Travis: use conda
Merge pull request #197 from ChrisBeaumont/conda

Travis: use conda for faster installs
Initial refactor of application into frontend-agnostic base class
Use commands
Data viewers take session objects as input instead of DataCollection
Undo/redo into gui
apply_roi, add_layer now commands
PEP8
test refactor
Updated gitignore
Limit number of undos
Fix contrast mode callback
Command tests
JSON States
Added scipy video embed
more state saving work
Exporters
PEP8
D3PO plugin