Added support for local json file upload, modified data classes

admin.py
	-nullified old handler stubs
	-added UploadJsonHandler, which will handle JSON uploads to the blobstore, and UploadPageHandler, which will provide the front-end to the upload

datatypes.py
	-Module model now has faculty, workload and strings for prerequisites and preclusions. These properties will provide additional data on the skill tree page.
	-AssignedModule no longer stores a key reference to modules, instead it only stores the module code
	-CachedModuleRepo date_retrieved renamed to time_retrieved, and changed into a DateTimeProperty
	-BugReport model added, this will allow users to report any inconsistencies spotted with our module data.

data.py
	-GetModuleHandler returns additional properties
	-GetSkillTreeHandler and SaveSkillTreeHandler now ensures AssignedModule is associated with a module code instead of the entity's key.

modulescraper.py
	-added support and logic for local NUSMods json files.
	-generate_module_list no longer takes in any parameters, and must be called separately from retrieve_modules. Note that time delay should be given between both methods to allow the datastore to commit properly.
	-updated logic with new Module properties.

scripts/skillTree.js
	-jsPlumb reconfigured to use straight line connectors, instead of flowchart's

templates/Home.html
	-central DIV updated to use a "center" class instead of relying on a CSS property.

templates/UploadPage.html
	-jinja2 template for the local file upload dialog. Supports asynchronous uploading with the jquery.iframe-post-form plugin

scripts/jquery.iframe-post-form.js
	-plugin for asynchronous upload