Fix theme functions

[kimpepper]

• Moves theme functions to twig templates and preprocess hooks
• Adds twig templates
• Fixes help page not showing

[Berdir]

This results in a container was serialized error for me in template_preprocess_token_tree(), looks like you're serializing everything in $variables, is that really necessary?

[Berdir]

Note that I simply fixed them for now by specifying 'function' in hook_theme(). As commented in https://www.drupal.org/node/1962358, I would recommend to refactor the whole display logic there before trying to make them twig templates, a lot of those will hopefully go away.

[jibran]

NW as per @Berdir's comment.