Add channel baseflow to chan dat

[FLO-2DJJ]

@FLO-2DKaren, @FLO-2DNoemi

You may now test the following features:

• [ ] Export CHAN.DAT with B lines for channel segments (*Export data (.DAT) files**).
• [ ] Import CHAN.DAT with B lines (from *Import data (.DAT) files**).
• [ ] Import B lines from CHAN.DAT in Import selected components files.
• [ ] Assign/edit Channel Baseflow in Schematized Channels Editor widget.
• [ ] Assign/edit Channel Baseflow in Schematized Channel Geometry dialog.

Take into account that the above applies to new projects created with new field ibaseflow in TABLE chan in the GeoPackage database, or from an updated old GeoPackage.

[FLO-2DKaren]

I can test this on Wed afternoon.