ENH: Rename namespace cosmologytools to cosmotk

Renamed the namespace to "cosmotk" for consistency.
ENH: Rename namespace cosmologytools to cosmotk

Renamed the namespace to "cosmotk" for consistency.

From: George Zagaris <george.zagaris@kitware.com>

git-svn-id: https://svn.alcf.anl.gov/repos/DarkUniverse/hacc/trunk/cosmotools@1603 952bdfbe-fa2e-45c0-a9ae-ac90d4a62daf
Merge branch 'svn/trunk'