Add ConceptSource.uniqueId

When working with MRRT templates (html templates for radiology reporting) the html header contains metadata sections about the used controlled terminology in the templates (SNOMED CT, RADLEX, ...).

This is might look like so (source radreport.org):

<coding_schemes>
 <coding_scheme name="RadLex" designator="2.16.840.1.113883.6.256" />
 <coding_scheme name="SNOMEDCT" designator="2.16.840.1.113883.6.96" />
 <coding_scheme name="LOINC" designator="2.16.840.1.113883.6.1" />
</coding_schemes>
<term>
 <code meaning="brain" value="RID6434" scheme="RadLex"/>
</term>

or (source IHE connectathon 2015):

<coding_schemes>
  <coding_scheme name="RADLEX" designator="2.16.840.1.113883.6.256" />
</coding_schemes>					
<term type="modality">
    <code meaning="computed tomography" value="RID10321" scheme="RADLEX" />
</term>

Currently the only way to find the ConceptSource matching the used controlled terminology in these templates is via the ConceptSource.getConceptSourceByName() which is case sensitive.

However as can be seen from the above code snippet MRRT templates and I'm sure also other standards dont always stick to the defined formatting of controlled terminology names once it is "RADLEX" which is actually what the official hl7Code would be and once it is "RadLex".

Current workaround is to get all ConceptSource's and match them in java ignoring the case.

SUGGESTION:

1. DB change

Add (optional,non unique) column `concept_reference_source.source_uid`

optional = to keep backwards compatibility
non unique = since some coding schemes (for example SNOMED) come in different versions which do have different (thus unique) hl7Codes (or coding scheme designators) but same UID values.

see
http://dicom.nema.org/medical/dicom/current/output/html/part16.html#chapter_8

2. Service Layer change

Add

`ConceptService.getConceptSourceBySourceUid(String)`

ADDITIONAL INFO:
http://www.ihe.net/uploadedFiles/Documents/Radiology/IHE_RAD_Suppl_MRRT.pdf
http://dicom.nema.org/medical/dicom/current/output/html/part16.html#chapter_8

defines <coding_scheme> attribute
name = a valid coding scheme designator. A reference list for well-known coding scheme designator is available in DICOM Part 16 Section 8.
designator = An Object identifier (OID) as specified in ITI TF-2x: Appendix B.