Docs: editorial cleanup, update examples and references, standardize formatting

* Rename Tutorial to Learn
* Fix typos, spellcheck
* Wrap consistently at 80 chars
* replace html with markdown
* Update Learn to match changes in mockup
* Make the sample JavaScript code pass the lint tests
* Editorial changes and updates to the deployment section
* Add a link to Rok's video at the Wine and Beer Sprint
* Getting Started: Editorial changes
* fix(Makefile) Typo on bundles
Merge branch 'tutorial-rework' of github.com:plone/mockup into bower-nix-fix
Docs: reformat using semantic linefeeds
Allow pkgs to be overrideable