Allow vl extensions for swmm views

[sjib]

Description:
For those who service data models other than VSA, value list extensions might be needed (i.e. AG-96 in the Canton of Aargau, which adds additional function_hierarchic for channels and drainage_system_* for catchment areas ). If one uses such extensions, the SWMM views won't work, as the hard-coded where clauses of the views have a different scope of options. By using the vsacode instead of the code in qgep_vl.*, these problems can be solved elegantly.

Related pull request:

• Allow vl extensions for swmm views