Compiling plumed with Cmake

[Iximiel]

I'm setting up the cmake compilation, using issues as a todo list:

• [x] #6
• [ ] #7
• [ ] #8
  • [x] #9
  • [ ] #10
  • [ ] #11
  • [x] #12
  • [ ] #13
  • [ ] #14
• [ ] #15
• [ ] #16
• [ ] #24
• [x] #25

These are a modernization of the installation interface:

• [x] #17
• [x] #18
• [ ] #19
• [ ] #20

[Iximiel]

I added config t the cltools, this makes easier test plumed with ctest in the build directory, without specifying the PLUMED_ROOT