Support local visualisation

[psyhtest]

Currently, the workflow visualisation widget can only be tested as part of http://cknowledge.org/repo. Allowing to launch it locally (e.g. ck start widget) would both simplify its development and make users happy, as they would be able to visualise all their local results before uploding any to cknowledge.org.

[ens-lg4]

The local visualization code has been added to ck-web repo and merged.