Updates list of block level elements

We regularly use ASIDE and HR in our editor. This change prevents Scribe's formatters from adding extra paragraphs when these elements are present.
Updates to include a full list of block level elements
Added the immutable dependency
Adds Immutable to the parameter
Corrects the dependencies on the page
Gets the Require path correct so the tests pass
Removes the flatten
Removes the Lodash flatten function
Makes the formatter lists immutable
Swaps the text formatters over to an immutable list
Stops initialising the immutable list with js arrays
Update Travis options to reflect the new environments they have available
Merge pull request #296 from guardian/rr-update-travis-env

CI: Travis update
Uses caches for downloaded packages to speed up the build
Merge pull request #297 from guardian/rr-use-caching

CI: Travis: Use caches for NPM and Bower
Merge pull request #295 from guardian/rr-immutable-js

Incorporate ImmutableJS
v1.1.0
Merge pull request #292 from DavidTobin/block-level-elements-update

Updates list of block level elements
Fixes missing dependency in the AMD example
Merge pull request #305 from DavidTobin/amd-example-fix

Fixes missing dependency in the AMD example