More forgiving bounds on semimajor axis prior

The default upper and lower bounds on the Jeffrey's prior on semimajor axis were giving unphysical results for widely-separated planets. Fixed.

orbitize/system.py

@@ -93,7 +93,7 @@ def __init__(self, num_secondary_bodies, data_table, system_mass,
 
         for body in np.arange(num_secondary_bodies):
             # Add semimajor axis prior
-            self.sys_priors.append(priors.JeffreysPrior(0.1, 100.))
+            self.sys_priors.append(priors.JeffreysPrior(0.001, 1e7))
             self.labels.append('sma{}'.format(body+1))
 
             # Add eccentricity prior