Disallow strings in limit choice.

[Jason Neal]

Currently, if a string is in the min/max limits it crashes as in #12.

File "/home/jneal/Projects/SWEETer-Cat/sweetercat/app.py", line 199, in plot_exo
  x1, x2 = float(request.form['x1']), float(request.form['x2'])
  ValueError: could not convert string to float: '11 Com'

Maybe this could wrapped in a try-except and if it cannot be turned into a float then it pops up a little box letting the user know their limits were invalid etc. (instead of crashing).

[Daniel Thaagaard Andreasen]

How about just setting the limits to the min and max values if it fails?

[Jason Neal]

That is probably the simpler solution.