Added Reference sequence class to indicate to which References a
SNPSet's coordinates apply.

Added a backref from SNP to SNPSet so that a SNP can find it's
context (SNPSet and Reference).

Added code to build References from iRODS metadata when a SNPSet is
loaded from an iRODS data object.

Updated the SNPSetPublisher to build References.
Added improved model of gender markers.

Added validation via type contraints.

Made the test qc.csv SNP manifest identical to the production one.
Merged in recent changes on devel to complete work on adding Moose
constraints.
Added argument checks to WTSI::NPG::Genotyping::Call::merge.

WTSI::NPG::Genotyping::Fluidgim::AssayResult:

Added is_empty method.

Renamed npg_ to canonical_ in cases where the thing being created is a
canonical version.

Renamed assay_position to assay_address to be consistent with
sample_address.

WTSI::NPG::Genotyping::Fluidgim::AssayResultSet:

Added size method.
Added sample_name method.
Added assay_addresses method.
Added result_at method.
Removed get_calls method.

WTSI::NPG::Genotyping::Fluidgim::Subscriber:

Now both creates and merges calls so that the assay addresses can me
checked across all the resultsets involved.

Modified other code to propagate the API changes.
Merge pull request #304 from keithj/snpset-reference

Compilation of changes to add call merging