Enhance getObservations to find observation with ref. dimension elements using Literals

[MichaelMartin]

if a dimension element is encoded such as : sdmx-dimension:timePeriod "2001-01-01"^^http://www.w3.org/2001/XMLSchema#date ; no observation will be received.

The corresponding getObservation sparql query is as follows: [...] FILTER ( ?d1 = "2008-01-01" OR ?d1 = "2009-01-01" OR [...]

but must be: [...] FILTER ( ?d1 = "2008-01-01"^^http://www.w3.org/2001/XMLSchema#date [...]

[MichaelMartin]

Literal values and its datatypes are selected via getComponentElements!