Add warning for odd GA result?

[Gabriel-p]

When the result of the GA shows something like this:

it's a good indication that the result might need to be reviewed. Perhaps advice running the GA again with a higher prob_min value.
The synth cluster in question had the following parameter values:

z = 0.02
log(age) = 7
dist_mod = 13.4 (3 kpc)
E(B-V) = 0.32 (Av = 1)

[Gabriel-p]

This can be quite tricky to implement for more complicated parameters distributions and I'm not sure it's worth the trouble unless it can be made simple.

[Gabriel-p]

The new 2-param density plots do not show this "density of checked solutions" map, so this is not an issue anymore.