Add optional order labeling

[Symiaq]

Adding the possibility to label trades would increase the possibility to document trades in an easier way for taxation.
In my case one finished trade consists out of three unique orders. Giving all of them the same ID would allow me to connect all three orders in a simple way. Especially when they aren't processed at the same time.

[Bi0max]

It's very important to be able to give your own ID to orders. Otherwise, it is hard to track orders.
It's also potentially dangerous, because order_id (assigned by Nash) can be lost, before it is saved to DB. Imagine, that after placing an order there was some DB connection error. Then order is then completely lost, because system does not know its ID.

[Bi0max]

@jankjr , could you pls check? it's a very important issue.

[MehdiSangtarash]

This will help me a lot too.

[MehdiSangtarash]

@localhuman @lucianoengel @alanpeabody any updates on this. it causes me problems on a daily, specially when there is connection time out.