View transmission as grouped tech outside map views

[brynpickering]

Instead of X1_to_X2 etc. in timeseries / capacity plots, there are times when it is nicer to see it grouped (e.g. all AC power lines together). This could use the same grouping as in the filtering.

Grouping of this kind could extend to other techs (e.g. all solar PV sub-types could be grouped together).

[sjpfenninger]

This is actually implemented now via network_grouping_param which defaults to tech_inheritance. This needs to be updated for pending naming changes in Calliope 0.7.