plot_utils: move common plotting functions out of thermal into a file of their own
diff --git a/cr2/thermal.py b/cr2/thermal.py
index 17614fc..1b3fc14 100644
--- a/cr2/thermal.py
+++ b/cr2/thermal.py
@@ -8,45 +8,7 @@
 import pandas as pd
 from matplotlib import pyplot as plt
 
-GOLDEN_RATIO = 1.618034
-
-def set_plot_size(width, height):
-    """Set the plot size.
-
-    This has to be called before calls to .plot()
-    """
-    if height is None:
-        if width is None:
-            height = 6
-            width = 10
-        else:
-            height = width / GOLDEN_RATIO
-    else:
-        if width is None:
-            width = height * GOLDEN_RATIO
-
-    plt.figure(figsize=(width, height))
-
-def normalize_title(title, opt_title):
-    """
-    Return a string with that contains the title and opt_title if it's not the empty string
-
-    See test_normalize_title() for usage
-    """
-    if opt_title is not "":
-        title = opt_title + " - " + title
-
-    return title
-
-def default_plot_settings(title=""):
-    """Set xlabel and title of the plot
-
-    This has to be called after calls to .plot()
-    """
-
-    plt.xlabel("Time")
-    if title:
-        plt.title(title)
+from plot_utils import set_plot_size, normalize_title, default_plot_settings
 
 class BaseThermal(object):
     """Base class to parse trace.dat dumps.