Revamped installation docs
Remove mention of vtkpython option to command line Tangelo
Removing special mention of VTKWeb and streaming; replacing with general discussion of plugins
Added text about http status code; reworked material about return types
Making documentation into a plugin.

Closes #416
Adding some text to new plugin doc page
Finished plugin documentation
Merge branch 'plugin-docs' into revamp-docs
Rearranged "core services" section to contain docs for all JS functions.

Plugin stuff will go in a separate documentation section, and maybe eventually
be moved to the plugins themselves.
Added skeleton bundled docs file, plus entries for Tangelo and Docs plugins
Added docs for stream plugin
Adding docs for vtkweb plugin
Added docs for Girder plugin
Fixing function signatures in vtkweb plugin docs
Added config plugin docs
Finishing bundled plugin docs
Merge branch 'bundled-plugin-docs' into revamp-docs
Swept through all docs to bring up to date.

Made a change in flickr app re how error instructions are shown (this will
require debugging after merging).
Merge branch 'revamp-docs' into plugin-system
Fixing error in hiding div contents properly