get/set mining addr (#1195)

get/set mining addr (#1195)

* get mining address

* Set mining addr

* go fmt

* Fix CI

* Avoid mining to null addr

* Prevent mining to null addr for api

* clean vendor

* format get/setMiningAddress func

* Update if statements format

* Combine

* go fmt

* clean GetMiningAddress()

* compact IF statements

* compact IF statements

* revert

* SetMiningAddress for non-local address

* combine

* go fmt

* private getProgramByAddress()

* Avoid mining to nil addr for get-work

* Roll back

* Fix CI

* tweak func seq