Use immutable object style

which allows object creator to set attribute requiring the dual index
split, and have this attribute specify the size of the dual indexes
Merge pull request #3 from dkj/dual_index

Dual index - Use immutable object style
Merge pull request #2 from wtsi-npg/devel

merge changes from wtsi-npg
dual index refinements

ensure max length of "Index" used by MiSeq is the split dual indexs' size,
and use custom default_expected_tag in preference to Index{,2} when using
samplesheet as source of LIMS info
pulled changes from remote jenniferliddle/dual_index; resolved conflicts, fixed failing test
Merge pull request #176 from wtsi-npg/devel

pull request from wtsi devel to master to create release 77.3
Merge pull request #177 from wtsi-npg/master

pull wtsi master (release 77.3) to wtsi devel
added list of top level directories for HiSeqX
Merge pull request #3 from wtsi-npg/devel

merge changes from wtsi-npg
Updated Changes file
Merge pull request #178 from srl147/devel

HiSeqX change to seq_instr_checker
added HX (HiSeqX) to $INSTRUMENT_PATTERN
Merge pull request #179 from srl147/devel

added HX (HiSeqX) to $INSTRUMENT_PATTERN
Merge pull request #180 from wtsi-npg/devel

pull request from wtsi devel to master to create release 77.4
added new version value for HiSeqX RunInfo.xml
Merge pull request #181 from srl147/devel

added new version value for HiSeqX RunInfo.xml
added changes for release 77.5
Merge pull request #182 from srl147/devel

added changes for release 77.5
Merge pull request #183 from wtsi-npg/devel

pull request from wtsi devel to master to create release 77.5
added code to generate HiSeqX runfolder names