Make key usage statistics and report unused keys at the end

[ethouris]

During the processing of the Silverball file the statistics can be made for every database that has been created in this file. Keys that undergo statistical processing are those that are used in the Silverball file, so only for processing of this file should the statistical recognition be performed, and accepting new keys turned off when postprocessing is done, although in postprocessing still the key usage is tracked. At the end of makefile generation, the tool should issue a warning about the databases and keys that were not used (set in user files, but not read by any faciliy).