pick up pre-installed dependencies if exist

[soonho-tri]

• [ ] need to write Find<PKG_NAME>.cmake for each dep
• Current deps: adept, easyloggingpp, ezoptionparser, ibex, json, nlopt, picosat, glpk, capd4

[soonho-tri]

This one is related to adding dReal to drake. In the process, we can make sure that dReal can be plugged into another project.

[jamiesnape]

You can use find_package for the latest masters of json and nlopt without writing a find-package file. For any CMake-based projects, I would try to upstream a *-config.cmake file.

[soonho-tri]

@jamiesnape, thanks!