decode URLs in staticHandler func (fixes #1565)

[bborgesr]

@jcheng5 is it this simple to fix the URL problem in #1565? I tested the example app and all three ways work now:

library(shiny)

addResourcePath("foo", "foo")

ui <- fluidPage(
  img(src="foo/foo.png"),
  img(src="foo/b a r.png"),
  img(src=URLencode("foo/b a r.png")),
  img(src="foo/b a r.png")
)

shinyApp(ui = ui, server = function(input, output) {})

given that these is a foo folder with a foo.png image and a b a r.png image.

[bborgesr]

Just because it's fun...

Before:

After:

[wch]

LGTM. NEWS item?