Fixed CDN URL for HTTPS requests

Fixes kasperpeulen/discourse-mathjax#7
Merge pull request #9 from lidel/master

Fixed CDN URL for HTTPS requests
Fix of broken Discourse.SiteSetting calls
Merge pull request #10 from lidel/site-settings-fix

Fix of broken Discourse.SiteSetting calls
Added Polish locale
Fix rendering in preview panel with a call from new Plugin API
Merge pull request #12 from lidel/preview-fix

Fix preview and add pl_PL locale
Allow configurable MathJax CDN asset URLs
Use single asset URL and allow configurable MathJax config setting
Merge pull request #13 from rookus/feature/configurable-cdn-urls

Allow configurable MathJax CDN asset URLs