Enhancements to league create/edit.

Leverage limit allows decimals and increments by 0.1

Changed text for time between redistributions from hours to seconds (as
is implemented on the backend).
Backend query for symbols.

<host>/symbols returns all the symbols scraped by all leagues (same for
individual leagues).
Added views for the histories of securities.
Refinements to the scraper.
Consolidated league create and edit into one view.
Leverage Limit -> Leverage Multiple