Make Staggered Orders default range -100x to + 100x

[MarkoPaasila]

For Staggered Orders.

First find out supposed center price, either automatically or manually #179. Calculate default values from that.

For 2 reasons:

1. The default range will be same for all markets.
2. The user won't have to do calculations

Both of these reasons means a better user experience, which is very important to us. It will help reduce errors and help people make less risky strategies.

100x is pretty conservative, and doesn't cost significantly more than 10x, so it can be considered a good default value.

[MarkoPaasila]

#237 should include this.