Handle FFTW support in both root used and in digitizer

DO NOT REMOVE THIS BOXED MESSAGE

Code in this merge request is subject to review by Code Owners.
The list of reviewers is posted in the comments section.
After all of the code is approved, please put a brief notice about it at the beginning of this message.

NOTE: Merging this code without getting it approved by Code Owners will result in suspending your developer rights!!!

This merge request will contain 3 fixes:
1) Request root to be built with FFTW support (non-simpath build);
1) Ensure that MpdTpcDigitizerAZ will fail with correct error message if no FFTW will be present;
1) Copy directory macro during the simpath build (issue #49 (closed)).

Closes #38 (closed), #49 (closed)