Add Type column to model.links (geo)dataframe

[aerispaha]

For several use-cases, it would be useful to be able to discern the type of link in each row that is returned by the swmmio.Model.links.dataframe (and geodataframe). As discussed here, we will likely benefit from an additional Type column in the links (geo)dataframe.

A similar thing is true for the swmmio.Model.nodes dataframe.

Proposal

Add a new column to swmmio.Model.links.dataframe and swmmio.Model.links.geodataframe that encodes the type of link in each row (e.g. Conduit, Pump, Weir, etc.)

Considerations

• Because this would be a special column, not derived from tabular data in the inp file, we should maybe consider a different style/syntax for the column name. Perhaps snake cased link_type
• We should be sure that this column doesn't clash with any existing column names. To achieve this, we might consider prepending the column name with dunders or a special swmmio_ string.
• We could also consider multi-indexing these dataframes, adding a link type index dimension. I expect this might cause some ripple effects though

[wraseman]

@aerispaha, I agree that it would be nice to be able to get the link or node type from the dataframe / geodataframe associated with swmmio.Model.links and swmmio.Model.nodes. One note is that I have noticed that sometimes the Type column does appear in the swmmio dataframe. I am not sure in what cases the Type column shows up (e.g., difference between SWMM, PCSWMM, etc.). I like the idea of creating a special column naming convention to avoid potential naming conflicts.

@bemcdonnell, any thoughts on naming convention?