sml: remove pods and add all the new types
sml: fix broken resolver tests
sml: more structural cleanups

- model is now a model element, with a full blown qname
- property is now using concepts
- improved documentation of model, property
- tidy-up terminology in qname
- remove references as we can use qnames for this
dia to sml: initial stab at updating the model
agile: open Comments seem to be trimmed
sml: refactor validator and get specs to compile

- commented out workflow for now
- major cleanup of validator as part of adding support for new
  stereotypes
- improve profile related documentation.
dia to sml: add ref to comment in profiler
dia to sml: start refactoring transformer spec
sml: remove the meta types enumeration
dia to sml: remove usages of the meta types enumeration
agile: open Register types for multiple models is misbehaving
agile: update Register types for multiple models is misbehaving
dia to sml: final push to get all tests to pass

- create a dia serialisation helper as a workaround problems with
  register types that stop us from loading two models with the same
  register types.
- add missing object flags to validator
- fix bug with keyed entity transformation in transformer
- add logging to profiler
- make processed properties collection a list instead of a vector as
  we don't really need random access
- improve transformer tests a lot, including adding a test for
  properties
diagrams: add initial support for operations
diagrams: update top-level documentation of the SML model
dia: fix linking issues in specs
sml: add initial support for operations

- write introductory documentation for SML
- remove last remnants of "pod" in SML
- add Operatable concept and associated machinery
dia to sml: remove last remnants of "pod" usage
sml: add tests for operation
sml: add support for visitor injection