Add Gantt widget to list

Add Gantt widget to list of widgets with keyboard navigation. Is this the only, new, one?
Fix router start / init documentation

Close #552
Merge pull request #555 from codylindley/patch-1

Add Gantt widget to list
Clarify that the bind operations are recursive

Close #539
Add docs for Splitter's collapsedSize pane property.
Add default values for Boolean/Object values
Split Sortable getting started into multiple files. Add sample scenarios sections and examples. Improve existing integration topics.
Add more sections and code samples to the Sortable Getting Started articles.
Add 'related' section in Sortable's overview topic.
Added upgrade wizard's warning page.
Merge pull request #558 from YanaMihailova/master

Added upgrade wizard's warning page.
Add Drawing API / Supported Browsers topic
Update Surface type documentation
Split the Overview topic in Overview/Basic Shapes
Merge branch 'drawing-api-prose'
Add TOC in Sortable's Getting Started article. Fix small wording and structure issues.
Change heading title
Add cleanFormatting tool to list of tools
Document when to use the updateIndeterminate method.
Add gantt overview help topic