Fix broken assets

Since switching to TypeScript our assets are broken due to the move of
app.js to the `./lib` subdirectory and the relative patch specified for
the public directory.

This patch solves the problem by adding a proper config element for the
path and referencing it in `./lib/app.js`.

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

lib/config/default.js

@@ -42,6 +42,7 @@ module.exports = {
   sslCAPath: '',
   dhParamPath: '',
   // other path
+  publicPath: './public',
   viewPath: './public/views',
   tmpPath: os.tmpdir(),
   defaultNotePath: './public/default.md',