Merge pull request #53 from czhang/master

Added item drop functionality.
Post-merge cleanup for syntax consistency. Minor grouping for repeated null item drop checks in base_player.js.
More post-merge cleanup. Minor refactoring for repeated code.
More post-merge cleanup (missed from first pass cleanup) for syntax consistency.
More post-merge cleanup. Refactored repeated code.
More post-merge cleanup. Removed unnecessary code. Fixed bug with discard item button not triggering correctly.
More post-merge cleanup. Refactored repeated code. Modified conditions to spawn unit weapon modal.
Added condition checks to not display unit portraits if unit does not have a portrait assigned to it (for inventory, trade, and stats screen).