cubicweb-seda #15045341 export simplified profile to SEDA 0.2 XSD [validation pending]

for SAEM compat

done in0.5.0
load left0.000
closed by<not specified>
patchAdd actions to download RNG or XSD of earlier SEDA versions [applied]Rename xsd_element into element_schema [applied]Refactor XSD export of old SEDA version to for later support of RNG export [applied]Refactor RNG export for later support of earlier SEDA version [applied]Basic export of simplified profile to SEDA 0.2 XSD [applied]Backport basic SEDA 1.0 export from the saem cube [applied]Prepare data files for export to SEDA 1.0 / 0.2 [applied]