Add features to plotting.surface_plotting and plotting.colormaps

[rcruces]

• added views to the default views of surface_plotting
• added colormaps

[ReinderVosDeWael]

Love the change to add other views, although this would also need to be updated in the docstrings.

I'm not sure I see the value of these additional colormaps. What's the use-case for gradients? As gradients are continuous I'd see little use to adding discrete colormaps, and the good people over at matplotlib have already provided every colormap under the sun including an analysis of their pros/cons. I'd prefer to rely on those rather than risking the feature bloat / additional maintenance. If it's for ease of access within MICA tools wouldn't BrainStat be the more appropriate toolbox as its more of a swiss army-knife?