Put all .cmake files in one directory

[pradeexsu]

Is your feature request related to a problem?
No, it's not related to any problem, it's about the convention that makes our code more structured.

Request Description
there are only 2 .cmake files Eigen.cmake and Boost.cmake, but in the future, there can be too many .cmake files. like.

• requires lp_solver.cmake for Remove lpsolve external libraries #141
• requires CodeCoverage.cmake Code coverage for volesti #139
• requires ClangFormat.cmake for issue Code formating #116

and in the future, there can be many .cmake files in volesti.

Solution Description
we can put all these similar kinds of .cmake files in a directory a cmake (we can call any suitable name), and add its path to our root CMakeLists.txt or where ever it's needed. in this way, our code will be more structured.