Todos: Cylinder app

[sgkang]

• add surface potential profile (use faked app res. calculation as we did in pseudo-section app)
  

• add center location of the cylinder

• fix color bar issue

[lheagy]

as well, in the plot of the potentials, please add a line that shows the half-space potential

[thast]

@sgkang , @lheagy , close the issues if you're happy!

[thast]

#44