Clean up and separation of trading system.
Rewrote the leverage limit system.
Rewrote trade system.

Trades now take a single object of {symbol: quantity, ...}. Negative
quantities are sell, positive are buy.

Front-end changed to reflect this.
Scraper now scrapes the entire S&P 500.

Scraper is also scalable to handle any number of symbols.
Bug fix, ticks are now stored properly.

Fixed by setting ask, bid, and/or ask to -1 if they are 'N/A' and then
setting the error flag to true.
Redistribution framework added.

League options for redistribution:
* redistribute agents: a flag that determines whether a league should
redistribute.
* first redistribution: the date/time at which the first redistribution
is to occur.
* redistribution period: the amount of time that must elapse from the
most recent redistribution to the next redistribution (designed to use
hours, currently uses seconds)

Currently, redistribution only takes $100 out of the agents' accounts.
League schema: all redistribution rules in one object.
Basic automatic selling of securities implemented.
Some cleaning up of ticks.
Merge branch 'master' of https://github.com/nwoodbury/tdf