Major improvements in GUI and deposit and withdraw commands.

* mudsketcher/mob-editor.lisp: mob-editor is improved and refactored to a separate
  class.

* mudsketcher/mudsketcher.lisp: mob-editor is improved and refactored to a separate
  class.

* mudsketcher/mudsketcher.ui: New dialogs for mob selection, dialog for shopkeeper.

* src/command.lisp: Hardening commands for wrong inputs, better deposit and
  withdraw commands.

* src/core-command.lisp: short-match-p function and tests for it.

* src/core-items.lisp: Minor improvements in item class.

* src/shop.lisp: Added classes SELLER and SHOP-ROOM.