Inlining of headers argument of genreflex in the dictionary

This is an additional feature. If not requested, the dictionaries work as before.
1) Enrich the RegisterModule interface of TROOT and TCling in order to take in the content of the header and not its path
2) Change TModuleGenerator in order to be able to generate the new dictionaries with the inlined header
3) Change rootcling to orchestrate the new mechanism. For now, if genreflex is called, the new dictionaries are used, if not, the old ones.
Correct the logic for choosing dict system at runtime