xsd-fu: C++ OMEModelObject template avoids DOM text content rvalue references

Needed to build with clang++ on FreeBSD, and fixes a type conversion error.
cmake: Add extra-warnings option
cpp: bioformats: SaveSeries can not throw on destruction
cpp: bioformats: Correct currentId assertions in FormatReader
cpp: Add test component

The test component produces an ome-test static library which all tests
should link against.  This depends upon gtest and provides headers which
tests may use.  This consolidates the test dependencies into a single
place, and allows the provision of common test facilities which may be
used by all tests.
cpp: test: xerces tests use ome-test and gtest
cpp: test: Add FormatReader testcase