plot_utils: move common plotting functions out of thermal into a file of their own
diff --git a/cr2/plot_utils.py b/cr2/plot_utils.py
new file mode 100644
index 0000000..c7d083b
--- /dev/null
+++ b/cr2/plot_utils.py
@@ -0,0 +1,44 @@
+#!/usr/bin/python
+"""Small functions to help with plots"""
+
+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)