Add observeEvent and eventFilter functions for handling events
Code review feedback, part 1
Add `position` parameter to `navbarPage`
Update to Selectize 0.11.2 with computedstyle fix

Fixes #596
Bump selectize version in html dependencies
Update NEWS
Better handling of observer errors

- Unhandled observer error no longer stops flushReact in mid-flush
- Observer errors are now warnings that include the observer label
- Session is explicitly being closed by Shiny instead of by httpuv

Also:
- session$close() is now public and closes the session
Add test for observer error handling
Remove unused withCallingHandlers()
Add global option for error handler function
fixes #605: send DT requests via POST instead of the default GET
Update shiny.R

Update link to shiny tutorial (http://shiny.rstudio.com/tutorial/)
Merge pull request #615 from seanchrismurphy/patch-1

Update shiny.R
Merge remote-tracking branch 'origin/pr/180'

Conflicts:
	NAMESPACE
	R/bootstrap.R
	R/reactives.R
	R/shiny.R
Update NEWS, bump version
Fix action button
Fix eventFilter logic
Fix documentation bug in ?validate
Remove eventFilter for now

After discussing with @trestletech, the semantics are just not right.
When using it with a renderXXX function, it doesn't actually stop
recomputation, so the only reasonable place to use it is in a reactive
expression, but if that's true then this is a terrible looking API.
Will replace soon with something better.
Merge pull request #610 from yihui/bugfix/DT-POST

fixes #605: send DT requests via POST instead of the default GET