Create generic Observation and Property for soil classification

[ldesousa]

Generic Property (glosis_pr:SoilClassificationProperty) as parent of:

• glosis_pr:soilClassificationFAOProperty
• glosis_pr:soilClassificationUSDAProperty
• glosis_pr:soilClassificationWRBProperty

Generic Observation (glosis_pr:SoilClassification) as parent of:

• glosis_pr:SoilClassificationWRB
• glosis_pr:SoilClassificationFAO
• glosis_pr:SoilClassificationUSDA

Factorise common properties where it makes sense.

[Montanaz0r]

this is done via PR https://github.com/rapw3k/glosis/pull/69. Awaiting approval

[ldesousa]

Done.