Use the Tmin,Tmax,Pmin,Pmax if specified in an Arkane job.

For the Chebyshev fitting it used to ignore the specified limits
and just use the lowest and highest points from the grid.
Chebyshev grid points aren't on the boundaries of the valid range,
so you'd end up with not the range you specified.
One consequence is network.py files created during an RMG job would not reproduce
the fits if you later ran them in Arkane.

Without this change, an RMG job would create
    TCHEB/ 300.000   2500.000 /
    PCHEB/ 0.010     98.692   /
but then when you run the network1_1.py file through Arkane you would get
    TCHEB/ 302.558   2335.460 /
    PCHEB/ 0.012     78.776   /

Author: rwest

arkane/pdep.py

@@ -132,9 +132,11 @@ def __init__(self, network,
 
         if Tlist is not None:
             self.Tlist = Tlist
-            self.Tmin = (np.min(self.Tlist.value_si), "K")
-            self.Tmax = (np.max(self.Tlist.value_si), "K")
             self.Tcount = len(self.Tlist.value_si)
+            if self.Tmin is None:
+                self.Tmin = (np.min(self.Tlist.value_si), "K")
+            if self.Tmax is None:
+                self.Tmax = (np.max(self.Tlist.value_si), "K")
         else:
             self.Tlist = None
 
@@ -143,9 +145,11 @@ def __init__(self, network,
         self.Pcount = Pcount
         if Plist is not None:
             self.Plist = Plist
-            self.Pmin = (np.min(self.Plist.value_si) * 1e-5, "bar")
-            self.Pmax = (np.max(self.Plist.value_si) * 1e-5, "bar")
             self.Pcount = len(self.Plist.value_si)
+            if self.Pmin is None:
+                self.Pmin = (np.min(self.Plist.value_si) * 1e-5, "bar")
+            if self.Pmax is None:
+                self.Pmax = (np.max(self.Plist.value_si) * 1e-5, "bar")
         else:
             self.Plist = None