rpc implement `setban`, `listbanned`, `clearbanned`

[coveralls]

Pull Request Test Coverage Report for Build 2858432506

• 3 of 171 (1.75%) changed or added relevant lines in 5 files are covered.
• 10 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.2%) to 51.682%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
btcjson/chainsvrcmds.go	3	17	17.65%
rpcclient/net.go	0	26	0.0%
rpcadapters.go	0	30	0.0%
server.go	0	30	0.0%
rpcserver.go	0	68	0.0%
<!--	Total:	3	171	1.75%	-->

Files with Coverage Reduction	New Missed Lines	%
peer/peer.go	10	76.24%
<!--	Total:	10		-->

Totals
Change from base Build 2858310889:	-0.2%
Covered Lines:	22481
Relevant Lines:	43499

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💛 - Coveralls