To enable this means the buildsystem will build all the applications
as well as the libraries.
Applications are 'hub' / 'txVulcano' / 'indexer' etc.
Default this one is turned off.
These are technically static libs, but not in any way shared libs.
They are used solely only by this repo and really only by the hub.
Most important, no header files are installed and basically none of
the normal rules for reusable libraries are applied to these files.
Duplicate the test_bitcoin file into the common dir,
I hope to remove the original in future.
Make the common dir a new static lib and create a new
qtestlib based unit test out of the old doublespend unit test.
tomFlowee
TomZ