Improvements to enable packaging

These are various improvements to enable packaging.  They were used in making the official Debian and Ubuntu packages

Packages normally should not contain copies of other libraries.  In this case, the DMTX library need not be included in the OpenRPT source and we should use libdmtx from the appropriate package (it is libdmtx0a.deb on Debian and Ubuntu)

Packages should produced shared libraries (not static libraries) for use by other packages.  In this case, OpenRPT is installed as a shared object for use by the PostBooks client.