Replace sdk.AccAddress with bech32 string

[alpe]

Resolves #306

[webmaster128]

Beautiful

[codecov]

Codecov Report

Merging #314 (0589dfa) into master (ca040da) will increase coverage by 0.12%.
The diff coverage is 26.79%.

@@            Coverage Diff             @@
##           master     #314      +/-   ##
==========================================
+ Coverage   17.53%   17.65%   +0.12%     
==========================================
  Files          35       35              
  Lines       10519    10592      +73     
==========================================
+ Hits         1844     1870      +26     
- Misses       8572     8607      +35     
- Partials      103      115      +12     

Impacted Files	Coverage Δ
x/wasm/internal/types/genesis.pb.go	0.66% <0.00%> (+<0.01%)	⬆️
x/wasm/internal/types/msg.pb.go	0.56% <0.00%> (+<0.01%)	⬆️
x/wasm/internal/types/proposal.pb.go	0.42% <0.00%> (+<0.01%)	⬆️
x/wasm/internal/types/query.pb.go	0.71% <0.00%> (+<0.01%)	⬆️
x/wasm/internal/types/query.pb.gw.go	0.00% <0.00%> (ø)
x/wasm/internal/types/types.pb.go	0.76% <0.00%> (+<0.01%)	⬆️
x/wasm/internal/types/types.go	21.62% <25.00%> (-1.91%)	⬇️
x/wasm/handler.go	42.85% <26.41%> (-9.98%)	⬇️
x/wasm/internal/keeper/test_common.go	83.39% <26.66%> (-3.33%)	⬇️
x/wasm/internal/types/msg.go	53.00% <36.58%> (-11.64%)	⬇️
... and 11 more

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