Introduce sitemap XSL template

Based on Yoast's All in One SEO plugin for WordPress implementation
Merge pull request #4559 from JohnONolan/sitemap-xsl

Introduce sitemap XSL template
URL safe base64 encoding

closes #3872
- updated base64 escaping to respect + and \
- updated base64 escaping to remove = during transport
- updated tests
Merge pull request #4554 from sebgie/issue#3872

URL safe base64 encoding
Move ugly debug to Settings  Labs

 closes #4534

- Adds new Labs route
- Wires route in settings page
- Move and rename debug templates and logic to labs
- Redirect /debug to settings/labs
Merge pull request #4560 from cobbspur/labs

Move ugly debug to Settings  Labs
[WIP] Tag Meta Screen
Working now