Option to use multiple stage/level input locations

[dvalters]

Similar to reach data mode (discharge), we want to be able to have multiple levels data points for input.

The logic for this could extend the stage_tide_inputs logic, or it could extend the reach input logic - i.e.

Extending Reach Mode logic

• Switch to flip between discharge and levels
• Multiple file support already there.
• Your input file would read the "discharge" column as either "discharge (cumecs)" or "river level (m)"
• Level get set by default as single pixel width (1D line)

Extending Stage Mode Logic

• Logic remains similar except:
• Switch to flip between local_datum and AOD datum.
• Current logic assumes AOD datum, i.e. the level is the elevation of the water surface, but many gauging stations report the local depth of the water relative to a local datum.
• Option to set a site datum?