Adding Implementation of Shop System (Prototype)

You will need to download the latest media files for this pull request to work. You can find it here (media_04-13-14.zip): https://bitbucket.org/chessmasterhong/wateremblem-media/downloads#download-346203

This pull request contains the following:

* Added prototype of shop system.
* Created Armory, Buy, Shop_Item and Exit Buttons for interacting with shops.
* Made the necessary changes to main.js and base_player.js for detecting and using the shop properly.
* Added a shop overlay entity. 

Things to come during the break:

* Adding 'sell' functionality to shop.
* Placement of buttons will be better.
* Will add a 'money' property to main.js in order to buy items/weapons.
* Looking into hooking up a type-writer style text generator. 
* Looking into a dialogue system. It will probably involve creating a new catalog called 'dialog_catalog.js'.
* I just realized that the weapon system isn't completely finished; I forgot that we need to give each class a weapon proficiency; we can't have assassins using lances and spells, etc. I'll take a look into working on that as well.
* Animations for other units need to be done, so I'll try and get as many as possible done.