pfSense

Fix repository config files

Add a new repo called next to point to 2.6.0-RC and reduce differences
between branches

Revert "Update master to 2.7.0"

This reverts commit ac7ec30f39a3069d3192a73b78e5977fc834482e.

Update master to 2.7.0

Rework repository config files

Instead of use version on file names, just call them repo, repo-devel
and repo-previous. Also, do not keep relying on variables, instead, use
versions hardcoded to make it easier when changing to newer versions.