Added support to read package files and and content

Also, parses the navigation document to set titles for the HTML files
Merge branch 'master' into github-refactor
Merge branch 'multiple-mediatypes' into github-refactor
Merge branch 'paths-in-ids' into github-refactor
Support loading image resources in HTML files
Merge branch 'multiple-mediatypes' into github-refactor
Remove the GET request by the browser when jQuery parses HTML with an IMG tag
Merge branch 'hotfix-dragging' into github-refactor
Merge branch 'toc-getchildren' into github-refactor
Use the mediaType in the container XML file

instead of hardcoding to OPF mediaType
Support basic navigation tree rendering

Does not remove duplicates or allow inserting after the current node.
Merge branch 'hotfix-dragging' into github-refactor
Merge branch 'master' into github-refactor
Added ToC serializing without rerendering
Listen to Collection `add remove` instead of a custom `change` trigger

Also, template uses hasChildren helper instead of the contents attribute
Move load semantics into load method
Removed `set` method by defining `parse`, removing `trigger('change')` and updating `load` logic.
Renamed `add` to `addChild` to avoid confusion with Backbone.Collection.add
Merge branch 'load-and-addchild' into github-refactor
Moved to private instance variable