add missing file header
encapsulate data types for Counters and DeltaCounters
add a mapping from SQL key names to counter fields
move external library configuration into root CMakeLists.txt
The libraries are needed in both the ./cvmfs and the ./test/unittests subdirectories
integrate database read/write with catalog::Counters
replace catalog statistics counters in the codebase
FIX: WriteToDatabase always failed
remove (preliminary) chunked file counters