new version

* remove files window on last file removal.
* implement exporting yang to new window.
* unify modal window for showing informations.
* implement yang to clipboard copying through external window since async requests coping
is not possible:
https://github.com/zeroclipboard/zeroclipboard/blob/master/docs/instructions.md#limitations
* add optional pretty format for yang output for better validation  on server side.
* add optional spacing format for 'unix_to_html' conversion when we want tabs
* reformat error/data responses to separate useful error reports (pyang)
* finish validation output
* prevent main module removal
* click to show statements window, focus out to remove it
* consolidate server response function and make it send json headers
* add revision date default value
* properly send yang files with multiline statements to server
* implement new module/submodule functionality
* remove custom gradients and use existing bootstrap classes
* save user yang files to 'public/yang' directory and setup 'cwd' properly so
  we could have proper validation with pyang and download of yangs - prepares
work for when multiple yang files are used
* remove existing nodejs modules and create package.json to pull them from npm

Signed-off-by: Petar Koretic <petar.koretic@sartura.hr>