Don't clear timers when runApp returns

The lifetimes of reactive expressions and observers can span multiple
runApp calls, so timers should as well.
closes #272: the argument ws_env was not used anywhere
bump the required version of httpuv to v1.2

this is to pull the changes to httpuv that enable shiny applications to run inside the rstudio viewer pane
Merge pull request #282 from rstudio/feature/httpuv-version

bump the required version of httpuv to v1.2
Merge remote-tracking branch 'origin/pr/276'

Conflicts:
	R/shiny.R
should pass a session object to invalidateLater()
add .csv to fileInput() to make it consistent with the tutorial (#280)
white spaces
add dataTableOutput() and renderDataTable() for the DataTables library

not yet done, but at least paging is working now
the ... argument is not really used
document renderDataTable() and dataTableOutput()
a simple implementation of global searching
make sure the data has two dimensions
disable default sorting
implement sorting; the very basic features are there now, but this still needs a lot of improvement in terms of details
now we can sort multiple columns: press Shift and click the column headers
index from 0, sigh
implement searching by columns
write a datatable output binding; the column names and action url are passed from renderDataTable() to the output binding
use the nicer bootstrap style