Client : wrote UI_MouseToInventory() to see if mouse is over the inventory
window, and which slot it is.
Data : updated 'default.cfg' to make default resolution be 800x600, and
separate settings into sections.
Game : worked on "invent_get" command, which will be sent from client when
user drops the dragged item onto the inventory window.
Game : more work on "invent_get" command...
Doc : added 'drag_n_drop.txt' file describing the protocol for handling
dragging and dropping objects.