[DO NOT MERGE] 1.4 release notes

Work in progress - please push or PR changes directly to wip-1.4 in this repo.

- [ ] document mod_auth_kerb #3312
- [ ] document chef #3699
- [ ] document proxy SSH puppetrun #3047
- [ ] document proxy Salt puppetrun #3732
- [ ] update Rails console docs to use foreman-rake console
- [ ] db:seed
- [ ] libvirt/dnsmasq providers
- [ ] REMOTE_USER attrs(?)
- [ ] mysql/mysql2
- [ ] proxy custom command
- [ ] Fedora 18 gone
- [ ] Hammer CLI release notes
- [ ] Debian plugin installation instructions
- [ ] RHSCL
- [ ] compute profiles
- [ ] Swedish