LP#1551090: Updating Makefile to accommodate ubuntu-xenial target.

LP#1551090: Updating Makefile to accommodate ubuntu-xenial target.

Changes to install pre-requisites for Unbuntu 16.04 (Xenial Xerus):

* Remove some redundancy in the extra debs lists.
* Add apache2 package to Makefile.install deb list.
* Add necessary connectivity for xenial deb installation.
* Move apache to the "install_extra_debs*" targets.
* Move debian_sys_config further down to compensate.
* Add apache2-dev dependency.
* Fix some whitespace.

Signed-off-by: Chris Sharp <csharp@georgialibraries.org>
Signed-off-by: Jason Stephenson <jason@sigio.com>