do_skims missing from tour mode choice #942
Description
Tour mode choice skims are stored in a number of wrappers used for easy use in the configs. For example, an od_skims wrapper exists for time-independent skims between the origin and the destination zone, and an odt_skims wrapper exists for time-dependent skims between an OD.
The do_skims wrapper was missing in tour mode choice. I bet this is because symmetry between an OD for time independent skims was assumed, however this is not necessarily the case. For example, bike times may differ between an OD pair due to elevation gain.
The missing do_skims object necessitated bike time skims that were not OD symmetric to be included as time-dependent and time-independent to the model. This reared its head in #939 (and is only a problem for sharrow because of the way that sharrow stores and accesses skims).
The fix is simply to make the do_skims object available to users in tour mode choice.