For Price Updates, use the conId internally instead of the symbol

[ellis]

This patch avoids conflicts for symbols in different marketplaces by using the conId where possible instead of the symbol.

In more detail:

• uses conId as a key where possible instead of symbol
• fixes errors on unsubscribe where the old subscriptions weren't removed from the internal map/array
• added more TickPrice strings for delayed prices
• added an interface for ProductUpdatesEvent
• changes a couple superfluous capitalizations

[ellis]

@ceddybi Just FYI, here's one of the things I'm using this library for:

The screenshot above shows a page I programmed to help me manage my stock "sub-portfolios" (i.e. resources allocated to different stock strategies) and diversification targets (diversification across sub-portfolios, regions, sectors, etc).

The other major aim, which I haven't started programming yet, is to help optimize my option strategy.

Ideally, I'd like to open-source this as well, but I'll need to remove the things that are currently hardcoded for my personal use. I don't expect it to be useful to end-users, because I definitely won't have time to make it user-friendly, but maybe it could be of some use to other programmers.