Moved vendored js/css into public/vendor and documented sources (#1484) (#2241)

* Cleaning up public/ and documenting js/css libs.

This commit mostly addresses #1484 by moving vendor'ed plugins into a
vendor/ directory and documenting their upstream source and license in
vendor/librejs.html.

This also proves gitea is using only open source js/css libraries which
helps toward reaching #1524.

* Removing unused css file.

The version of this file in use is located at:
  vendor/plugins/highlight/github.css

* Cleaned up librejs.html and added javascript header

A SafeJS function was added to templates/helper.go to allow keeping
comments inside of javascript.

A javascript comment was added in the header of templates/base/head.tmpl
to mark all non-inline source as free.

The librejs.html file was updated to meet the current librejs spec. I
have now verified that the librejs plugin detects most of the scripts
included in gitea and suspect the non-free detections are the result of
a bug in the plugin. I believe this commit is enough to meet the C0.0
requirement of #1534.

* Updating SafeJS function per lint suggestion

* Added VERSIONS file, per request

Makefile

@@ -285,9 +285,9 @@ public/css/index.css: $(STYLESHEETS)
 
 .PHONY: swagger-ui
 swagger-ui:
-	rm -Rf public/assets/swagger-ui
+	rm -Rf public/vendor/assets/swagger-ui
 	git clone --depth=10 -b v3.0.7 --single-branch https://github.com/swagger-api/swagger-ui.git $(TMPDIR)/swagger-ui
-	mv $(TMPDIR)/swagger-ui/dist public/assets/swagger-ui
+	mv $(TMPDIR)/swagger-ui/dist public/vendor/assets/swagger-ui
 	rm -Rf $(TMPDIR)/swagger-ui
 	$(SED_INPLACE) "s;http://petstore.swagger.io/v2/swagger.json;../../swagger.v1.json;g" public/assets/swagger-ui/index.html