Custom item pool feature

This is the starting point for the new custom item pool feature that will let users specify the item pool. It is functional, perhaps due for some minor tweaking and definitely needs more testing. The command line side is bad, just two parameters that hopefully don't do anything under any circumstance if the user tries to use them (don't really intend to support a command line version of this feature); maybe there's a better way to let the command line ER work in general without having any opportunity to activate this feature. The GUI should probably show the user the sum of the current item pool out of 153 so the user knows how to size the item pool more easily, but that's a todo.

EntranceRandomizer.py

@@ -163,6 +163,8 @@ def start():
                              Keys (and other dungeon items) are no longer restricted to
                              their dungeons, but can be anywhere
                              ''', action='store_true')
+    parser.add_argument('--custom', default=False, help='Not supported.')
+    parser.add_argument('--customitemarray', default=False, help='Not supported.')
     parser.add_argument('--nodungeonitems', help='''\
                              Remove Maps and Compasses from Itempool, replacing them by
                              empty slots.