add snippet to prevent single word lines

[yuvilio]

This PR adds a js snippet to prevent "widowed" (one word) lines to help improve their readability.

Notes

• The snippet is already in use on a few of the sites bubs is being used with.
• The tags it applies to can be adjusted depending on need.
• You can also opt out of the snippet on specific instances of the tag by adding a no-widont class to that tag.