DV_CODED_TEXT mapping, map code to value if no display provided

[SevKohler]

Map the code to the value in openEHR if no display is provided.
Better would be a termserver resolving that.
OpenEHR value (freetext) is mandatory therefore at least the code should be mapped if nothing else is provided .

[SevKohler]

fixed in https://github.com/SevKohler/openFHIR/tree/test_fall