[command] Fix section parsing algorithm of 'Execute SPARQL Query'

+ It should exclude lines containing section markers
+ Start line numbering at zero and thereby fix bug in section parsing
algorithm
[command] Syntax validation should not be limited to source.turtle documents

+ Use rapper parser 'guess'
+ Change helper methods
+ Fix three minor bugs that were just discovered
[command] Validate syntax / Do not escape file URL

Do not escape file URL because Rapper does it neither and we need the
file URL for filtering/guessing tasks.
[command] Add query log to 'Execute SPARQL query'
[command] Enable resource documentation also inside SPARQL scope