Add new autoclose = TRUE param to dateInput() and dateRangeInput

[bborgesr]

Closes #1969 and its much older duplicate, closes #173. I also made this option the default, since that seems to be the common use case. Here's a demo app:

library('shiny')

shinyApp(
  ui = fluidPage(
    dateInput("date1", label = "Autoclosing"), # new default
    dateInput("date2", label = "Manual closing", autoclose = FALSE),
    dateRangeInput("date3", label = "Autoclosing"), # new default
    dateRangeInput("date4", label = "Manual closing", autoclose = FALSE)
  ), 
  server = function(input, output, session) {}
)