Email Configuration section added

Content pulled from http://projects.theforeman.org/projects/foreman/wiki/Email_configuration and entered in with proper formatting.
Merge pull request #280 from ntent-ashton/patch-1

Email Settings Documentation
Fixed formatting mistake

I used the wrong version of MarkDown, broke the live manual's formatting.
Merge pull request #281 from ntent-ashton/patch-1

Fixed formatting mistake
Documentation: Fix small type DHS -> DNS
Merge pull request #282 from Spredzy/fix_typo

Documentation: Fix small type DHS -> DNS
Per-OS installation instructions

Fixes various things like CentOS 7 SCL instructions, per-Debian/Ubuntu release
sources, more detailed instructions for RHEL channels and explicit Puppet Labs
repo instructions.
Copy 1.6 to 1.7
Rename 1.6 to 1.7
Wipe 1.6 release notes
Add warning about 127.0.1.1 on Ubuntu, fix grammar
Add sprint 30 demo
Adding ABRT plugins deep dive
Merge pull request #283 from lzap/dd-abrt

Adding ABRT plugins deep dive
1.7 release notes: sprints 27-30
Remove SELinux upgrade warning
1.7 headline items, upgrade notes
Fix text video reference and tidy up CSS
More sprint 30 release notes
Add 1.7 contributors