Write Reader for MATLAB File

[rouille]

Write the MATReader object that will generate the grid from the MATLAB file created by the MATLAB script that runs MATPOWER/MOST. Note that a similar file will be generating by REISE.jl. Things to be done in addition to write the reader:

• Refactor the Scaler object to account for changes in the gencost attribute of the Grid object.
• Modify prepare_mpc_file method in the SimulationInput object in order to pass all information needed to case.mat in order to retrieve the grid after simulation.
• Modify InputData object to load the MATLAB file from local folder or from the server.
• Modify get_grid method in the Analyze object to retrieve the grid using the MATReader object.
• Perform a test run.

[danielolsen]

The PR for generating this file in REISE.jl is here: Breakthrough-Energy/REISE.jl#11

Modifying the parameters of the mpc.gen table is fairly straightforward, but modifying mpc.gencost is less so. The original parameters contain more information than the linearized ones, so we probably want to preserve them somewhere. Should mpc.gencost contain the original parameters, or the linearized ones? Whichever set goes into mpc.gencost, where should we store the other one?