(Exchanges) Introduce validation method and small updates (#565)

* Remove pointer reference

* Fix portfolio withdraw tests

* Add nil protection in validator method to reduce prospective panics and for future outbound checking

* Updated tests

* ch order var to not ref package

* rm comparison

* Add order ID validation check

* Add exchange name validation check

* Add in test details

* fix tests

* fix linter issues

* linter issues strikes again

* linter rabbit hole

* Addr nitterinos

* Add validation variadic interface to define sets of functionality check POC

* didn't want to add an amount other than 0, didn't want to add address to exchange withdraw, didn't want to whitlist, can change if need be

* add coverage

* Add validation method options for exchange wrappers and abstracted validation into its own package

* Add validation code for structs in exchange template generation

* remove extra validation call as this is done in wrapper

* fix niterinos for examplerinos

* Add template to documentation tool and regenerated documentation

* Addr niticles

* Fix tests due to validation update

* Add more validation checks for modify/submit orders

* update tests

* fix more tests

* Add asset type to submit variable in tests and rpc call. Regen funcs.

* Add field to modify struct in tests

* applied field asset to cancel struct across project

* fix woopsy

docs/EXCHANGE_API.md

@@ -63,6 +63,7 @@ supplied meet the requirements to make an authenticated request.
         OrderType: order.Limit,
         Price:     1000000,
         Amount:    0.1,
+        AssetType: asset.Spot,
     }
     resp, err := b.SubmitOrder(o)
     if err != nil {