Define (balance) constraints tables

[abelsiqueira]

The way that the (balance) constraints work is by asset. The table defines the necessary information for each of these assets. In the current implementation, one of the columns of this table is the JuMP expression with the incoming flow (and one for the output, and possibly more for extra stuff). Constructing the incoming and outgoing flows is a huge issue. It was slow and we had to figure out a nice way to do it. Furthermore, if we want to use an external table format, we can't save the expressions in the table. So the format will need to be changed. Whatever we do we must be sure that it doesn't compromise performance.

Possible implementation:

• Create a TulipaConstraint struct similar to TulipaVariable
  It should hold the indices table, the variables container, and at least for balance constraints, it could hold the incoming and outgoing expressions. Details might be different
• Also create t_highest_... tables (see file tmp.jl)
• Delete constraints_partitions and use TulipaConstraint instead
  By using (and extending) the tables created in Create all variables directly from connection and independent of dataframes #926 for lowest and highest resolution, we can create the indices of the constraints and store them in TulipaConstraint
• Create constraint tables for variables (e.g. :storage_level_intra_rp)
• Move constraint indices defined in dataframes to TulipaConstraint (see file model-preparation.jl)