Homepage speed enhancements

[benlk]

This is more of an ongoing project, but:

• [ ] dequeue job board assets on the homepage, and file bug report with job board plugin maintainer about assets being improperly enqueued
• [ ] lazyload the member images
• [ ] use image srcsets where possible
• [ ] review all other enqueued assets and dequeue them from the homepage if appropriate
• [ ] use (reference) LESS imports for homepage styles #83

For https://secure.helpscout.net/conversation/692975286/2744/?folderId=1219602