Add first iteration of Core methods

[lozand]

There will probably be more things to add here, but for now, we should include the following:

• Basic GET methods
• Some UPDATE methods
• BUY stocks
  • Needs to check for how much money you have before OKing the transaction
  • Needs to audit the transaction
• SELL stocks
  • Needs to audit the transaction
• VALUE portfolio
• Display how much CASH the user has