DWDS/Dialing Concordance Code

+ refactored old ConcHolder.* into ConcSessionContext.*, ConcSession.*
- ConcSessionContext: shared global data (cache)
- ConcSession: thread-local data (everything else)
- ConcHolder: now just a typedef alias for ConcSession

* factored out QueryResult, CQueryResultIndex from ConcHolder.h to new QueryResult.h

+ crashes as expected running client-threads with 'real' queries
- TEST: ./bin/ddc_daemon restart --nofork --stderr --server etc.pnn/ddc_server.cfg --local etc.pnn/ddc_local_corpora.cfg --log trace -t 2
- CLIENT: ./src/ddc_daemon/ddc-bench-multi.perl -p=52120 -c -q 'der die das' 'er sie es' 'auf von mit' -n 4
- CRASHES: in ~QueryNode(), called from via DeleteTree in shared CQueryCompiler (should be local)

+ got server options file-parsing working, renamed weird 'ProtocolDensity' stuff to more intuitive 'LogLevel' (with backwards-compatible typedefs)

+ ddc_daemon seems working in thread mode with nWorkers=1; serial mode (nWorkers=0) also still works

+ branch server threading works for status,info
- but no data returned from queries (ought to be safe with nworkers==1)

+ integrated StartClientThreads() call into CDDCServer::RunThread() [now virtual]

+ moved server thread stuff into ConcordDmnLib/ServerThread.(h|cpp)

+ moved ddcThread.*, ddcThreadQueue.* to src/common/; built in CommonLib

+ threadme2: thread pool working for dummy server