Create backend logic to parse contents of URL

[jeff1evesque]

We will create python/xml_retriever.py as a generic class that will take two parameters:

• the URL of the xml document to parse
• an object containing the xml attributes to parse from the xml document

This class, after being instantiated will return an object. This return object will be the important xml attributes we wanted to parse for (as defined by the second parameter of this class).

[jeff1evesque]

The above remarks are no longer valid, for the same reasons as follows:

• Define validation on content provided by URL #1290 (comment)

Therefore, we need to create generic logic, that will parse the contents of a webpage, for the following cases:

• csv
• xml
• json