MPC parameterization and intuitive tuning

[avikde]

Learnings about parameters while working on #10

• tuning parameters: weights, N, dt, eps_abs, eps_rel
• longer N => problem harder to solve => infeasible result more likely
• shorter N and/or longer dt => instability more likely
• eps_i lower => infeasible more likely (TODO: needs more testing)

Todo:

• reason about units for wxi, wui and reduce those to two scalars?
• reduce the number of parameters by scaling weights

From working on #33:

It is sensitive to:

• dt
• N
• weights in hover phase

Transition to hover phase: should switch to sequential composition