Remove starting inventory, adjust player init, etc.

Decided to do away with any starting inventory, restored the
"get_num_heavy_items_owned" function, and modified the
"get_nth_item_type", "menu_select_callback", and
"menu_get_num_rows_callback" functions to handle varying numbers of
heavy items in inventory. Also removed an unnecessary (and problematic
now that ENTRANCE isn't a cell type) test for empty cells from
"draw_cell_contents", adjusted some NPC graphics, made a few minor
memory-saving changes to "init_location", and changed how max. energy
and energy loss per action are determined.