Implemented ambient field calibration tool.

src/exceptions.py

@@ -0,0 +1,13 @@
+class ProxyNotOwnedException(Exception):
+    """Should not occur in correct operation. For whatever reason, this means the proxy was invalidated."""
+    pass
+
+
+class DeviceAccessError(Exception):
+    """General error indicating that HW access failed."""
+    pass
+
+
+class DeviceBusy(DeviceAccessError):
+    """Error thrown when the HW proxy (i.e. access) cannot be acquired"""
+    pass