semver sorting: make "version" column UNIQUE

This increases performance and avoids duplicate entries
which could cause problems if the position is ever com-
pared using the < or > operators instead of <= and >=.
fix semver filters for unknown versions

When restricting versions, the code failed if the specified
versions did not exist in the data set as they had no known
position in the sorted version list. Therefore, do now pass
them to SortHelper which includes it in the data set before
sorting.