Fix plotting of modes

[jguarato]

Pull Request created to make corrections related to the plotting of modes in the Results class:

• Removal of duplicate information related to whirl direction, which was inconsistent because the colors were not in accordance with the whirl direction shown in figures.

  • Only information from the Shape class was kept.
  • Unused methods were then removed.

• Some adjustments were made to the _eigen method of the Rotor class.

  • To avoid constant changes in the plotting of the modes in each simulation, due to the random nature of the solver initialization, the parameter v0 of the las.eigs function was set with a fixed array of values.
  • A limitation related to the amount of eigenvalues ​​to be found was applied when sparse = True.

• As tests were carried out, the appearance of bugs and warnings were also corrected.