v0.19.0

This release has pretty big changes in the way the store and connected components
works.

Changes

QWeb: support XML documents (already parsed) as argument to the addTemplates method (in
addition to strings)
ConnectedComponent: separate props into props and storeProps
ConnectedComponent: add dispatch method
Component: simplify render method signature (and rendering process)
Store: merge actions and mutations
router: add documentation
playground: add window management system example
Component: improve mount/remount behaviour, add renderBeforeRemount argument
to mount