rpc: support stringified address in getnep5balances RPC

[fyrchik]

Fix #1143 .

Also extend getnep5transfers.

[codecov]

Codecov Report

Merging #1146 into master-2.x will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@              Coverage Diff               @@
##           master-2.x    #1146      +/-   ##
==============================================
+ Coverage       67.95%   67.96%   +0.01%     
==============================================
  Files             159      159              
  Lines           15551    15556       +5     
==============================================
+ Hits            10567    10573       +6     
+ Misses           4463     4462       -1     
  Partials          521      521              

Impacted Files	Coverage Δ
pkg/rpc/request/param.go	78.89% <100.00%> (+1.01%)	⬆️
pkg/rpc/server/server.go	81.61% <100.00%> (ø)
pkg/core/mpt/trie.go	92.43% <0.00%> (-0.43%)	⬇️
pkg/rpc/client/wsclient.go	85.71% <0.00%> (+1.36%)	⬆️

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[AnnaShaleva]

Should we also add support of this feature to RPC client?

[fyrchik]

@AnnaShaleva GetNEP5Balances works with raw hash so it is ok. Maybe we should update GetNEP5Transfers to work with raw util.Uint160 type too.

[roman-khimov]

func (c *Client) GetNEP5Balances(address util.Uint160) (*result.NEP5Balances, error) 
func (c *Client) GetNEP5Transfers(address string) (*result.NEP5Transfers, error)

Seems to be OK already (although technically they could both be util.Uint160, but let's not change it for Neo 2.