Resolve "Social media buttons contain broken text"

Closes #16 (closed)

This MR basically applies the following edx-platform pull request to our theme locally:

https://github.com/edx/edx-platform/pull/26393

This is necessary for two reasons:

1. We're not running the most recent version of edX
2. Even if we did, it's likely that merging that PR will take long and then it will be included in the next major release