Add privacy and ToS links

To be GDPR compliant we need to provide privacy statement. These should
be linked on the index page. So as soon as a document exist under
`public/docs/privacy.md` the link will show up.

Since we already add legal links, we also add Terms of Use, which will
show up as soon as `public/docs/terms-of-use.md` exists.

This should allow everyone to provide the legal documents they need for
GDPR and other privacy and business laws.

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

lib/response.js

@@ -2,6 +2,7 @@
 // response
 // external modules
 var fs = require('fs')
+var path = require('path')
 var markdownpdf = require('markdown-pdf')
 var shortId = require('shortid')
 var querystring = require('querystring')
@@ -75,7 +76,9 @@ function showIndex (req, res, next) {
     allowPDFExport: config.allowPDFExport,
     signin: req.isAuthenticated(),
     infoMessage: req.flash('info'),
-    errorMessage: req.flash('error')
+    errorMessage: req.flash('error'),
+    privacyStatement: fs.existsSync(path.join(config.docsPath, 'privacy.md')),
+    termsOfUse: fs.existsSync(path.join(config.docsPath, 'terms-of-use.md'))
   })
 }