Modified several mockup files; added basic skill tree functionality.

mockup/css/custom.css:
	-Modified padding declaration for #left_panel; has no real effect.

mockup/css/main.css:
	-added declaration for semester DIVs
	-changed positioning calculation of moduleBoxes to absolute
	-added relative positioning to the SkillTree DIV.

mockup/index.html
	-fixed old references to css files
	-Added a semester div, will be replaced by dynamic addition of semesters
	-removed all static moduleBox DIVs

mockup/js/modules.json
	-Added missing CS1020 module

mockup/js/script.js
	-Added resize event handler to resize module list to 'fill' remaining space.
	-Modified double-click function of modules for easier reading; modules are now stored in an arbitary module variable from getModule.
	-when modules are added, all existing prerequisites already placed in the skill tree will connect to them.

mockup/js/skillTree.js
	-Arrow overlay added to module connections
	-connections to and from module boxes are now infinite
	-All major logic from original js file commented out
	-logic transferred to custom jQuery plugin functions moduleBox(), connectBottomTo() and connectTopTo().
		-moduleBox() adds connector endPoints to a given div, as well as the 'moduleBox' class.
		-connectTopTo() and connectBottomTo() connects the element(s) to the moduleBoxes of the given id parameter.
	-resize event handler added to dynamically resize the skill tree DIV to 'fill' the remaining space.
Added basic semester drag-and-drop functionality.

mockup/css/main.css
	-specified z-indexes for skill tree elements; this should prevent invalid overlapping.

mockup/js/script.js
	-added num_semesters property to the myGlobal variable to keep track of the number of semesters currently available.
	-cleaned up resize code

mockup/js/skillTree.js
	-made semester DIVs 'droppable' with simple logic
	-cleaned up resize function
	-added skillTreeView div to resize function; its height will be the same as skillTree's min-height.