devel/cmake: Create a meta-port for CMake

Create a meta-port for CMake to make it easier for the end user and
better handling of build dependencies.

This pushes devel/cmake into /devel/cmake-core and splits manpages and
its dependencies to /devel/cmake-man

Approved by: kde (tcberner)
Differential Revision: https://reviews.freebsd.org/D34957