LP#1390138: Updating Upgrade and Install docs for 2.7

LP#1390138: Updating Upgrade and Install docs for 2.7

Upgrade Docs
- Bolded all linux user names so the format matches the install docs.
- Added note about postgres 9.3 being recommended version and 9.1 being the minium version.
- Added Fedora to list of supported linux distros so it matches install docs.
- Added a note about the different apache config files for apache 2.4+ vs Apache 2.2.
- Added a link to troubleshooting section of install docs.

Install Docs
- Added notes about 9.3 being recommened version of postgres and 9.1 being the minimum.
- Changed opensrf version from 2.3.0 to 2.4.0

Signed-off-by: Josh Stompro <stomproj@larl.org>
Signed-off-by: Ben Shum <bshum@biblio.org>