fix tww_symbology_inflow_prio

[cymed]

When handling discharge points into culverted water bodies, we want the symbology to be "green" instead of "blue". Therefore, we have anadditional field tww_symbology_inflow_prio, Theis field was mistakenly created on function_hierachic instead of usage_current. This PR fixes that

[sjib]

@urskaufmann is this change correct?

[cymed]

          > Labeling is ok Symbology: I'm not sure. Manhole symbology depends on the connected channels. First prio: outlet-channel (outlet of the main node). If there are 2/more outlets (which is really an exception), then it's the PAA-channel, that matters. If there are 2/more outlet-PAA-Channels, then it's the usage_current (tww_symbology_order in tww_vl.channel_usage_current). If there is no outlet, then it depends on the inlets and here again the same rules: first PAA before SAA, then usage_current with the same prio as in the outlet case. I do not see the case when to use a separate inflow_prio.

Symbology is exactly what is currently implemented. We prioritise inflowing channels with discharged wastewater over outflows so we can symbolise discharge points into culverted water bodies with the _usage_current "discharged_wastewater". If there is no incoming channel with discharged wastewater, we prioritise by outgoing over incoming and function_hierarchic over usage_current

Originally posted by @cymed in #539 (comment)

[cymed]

@urskaufmann is this change correct?

#539 (comment)_

[sjib]

Great - thanks!