WikiEducator assets over SSL

[Jim Tittsler]

Currently the script hard codes http: in several places where it sideloads assets from WikiEducator. These should be changed to either:

• use protocol relative URLs
• force https:

This needs to happen before forcing SSL on WordPress instances containing courses.

[Jim Tittsler]

Use https or // to sideload.

Force https (or use protocol relative references) to allow enabling SSL on deployed WordPress site.

Addresses #30

→ <<cset c469d4e5f14a>>

[Jim Tittsler]

It may make sense to force SSL rather than relying on protocol relative URLs, but for now, this is resolved.