Currently the setup.sh file which is generated by catkin build is very slow because it must execute setup.sh --extend for each leaf package and each of those leaf package's run depends recursively (excluding overlap from build depends). On a large workspace, like hydro-desktop_full, 250 packages means sourcing ~188 setup files.

Because of the way the devel space is created we can theoretically create a faster single setup.sh which builds the combined devel space in one invocation.

Related: #24