Fix solving objective functions of form "p = x+y+2" or similar

[invisi-splat]

There's an issue with the current version of the LP calculator - inputting an objective function with a constant in it (e.g. M = m-4 or p = x+y+2) doesn't correctly calculate the final value of the objective variable. It instead creates a column with an empty variable name in the tableau.

I've fixed this by moving this constant to the RHS of the objective row. The algorithm then continues as usual.