Make trick (Python package) a namespace package

Namespace packages are a mechanism for splitting a single Python
package across multiple directories on disk. With the addition of
$(TRICK_HOME)/pymods/trick, there now exists a package named 'trick' at
$(TRICK_HOME)/pymods and in each SIM_* directory. This change allows sims
to import modules from both locations.

Refs #365

trick_source/sim_services/InputProcessor/IPPython.cpp

@@ -103,6 +103,7 @@ int Trick::IPPython::init() {
      "import struct\n"
      "import binascii\n"
      "sys.path.append(os.getcwd())\n"
+     "sys.path.append(os.path.join(os.environ['TRICK_HOME'], 'pymods'))\n"
      "sys.path += map(str.strip, os.environ['TRICK_PYTHON_PATH'].split(':'))\n"
      "import trick\n"
      "sys.path.append(os.getcwd() + \"/Modified_data\")\n"