The CMakeLists.txt file of the catalogue directory instructs
cmake to generate SqliteCatalogueSchema.cpp, by combining
the contents of the SqliteCatalogueSchema.before_SQL.cpp with the
contents of catalogue_schema.sql.  This means the
SqliteCatalogueSchema.before_SQL.cpp file is not compilable.

The purpose of the SqliteCatalogueSchema structure class is to
isolate the "non-compilable" issues into a small and encapsulated
compilation unit, namely SqliteCatalogueSchema.o, so that the
remaining business logic can be implemented in the non-generated
and compilable SqliteCatalogue.cpp file.  This means that IDEs can
work as normal with SqliteCatalogue.cpp, whereas they will struggle
with SqliteCatalogueSchema.before_SQL.cpp which is therefore
intentionally small.

Moved all of the classes in middletier/common to the scheduler directory because most of them are specific to the scheduler.  Please feel free to move those that are no so specific elsewhere.

middletier, itself separated in interface, SQLite, objectstore and
shared tests.
Moved all utilities (exceptions, threading...) to a shared utility
directory.
Created a single, shared unit test from all the scattered ones.

License comment is no longer filtered out by doxygen when generating web pages of the individual source files.