Made statics in GctFormatTranslate* classes const

Using C++11 initializer lists allowed all the statics to be converted
to const. This avoids thread-safety issues.
Made GctRawToDigi a stream module

All the statics accessed by GctRawToDigi are now const. This class
not being thread-safe was a performance bottleneck for the threaded
framework.
Merge pull request #3991 from Dr15Jones/makeGctRawToDigiThreadSafe

Make GctRawToDigi thread safe