improve display of existing files in file input

* show filename with link to download in new window
* change the global handleClick to ignore links with a target
* add the word 'replacement' if a file exists to make it clearer that it will be replaced
Merge pull request #520 from ENCODE-DCC/forms-fix-file-input

improve display of existing files in file input
Merge remote-tracking branch 'origin/master' into 2489-audit-search