Main event loop and maker logic

[da-kami]

Since this is ever-growing, I would merge the current state and then extend it. (I am branching off this state and work on rate/balance update logic.)

Note that I added dai_balance() to the ethereum wallet for convenience.

Implemented:

• Logic for handle take requests (buy and sell)

Outlined:

• Initialisation (TODOs for config plugs there)

To be added:

• Logic for update rate
• Logic for update balance

[da-kami]

bors r+

[bors[bot]]

Timed out.