Make site more small-window friendly

Re-write code using bootstrap CSS to allow for responsive layout on
variety of devices currently used in the district.

Focus will be small-screen mobile first, then large screen desktop.

- [ ] Maintain current look and feel
- [ ] Reflow design on small screens/mobile devices
- [ ] Implement same CSS layout for [pennmanor/PMExtension](https://github.com/pennmanor/PMExtension)