Add pagination to grpc queries

[alpe]

Resolves #242

New:

• New second index for contracts by code id and creation marker
• Contract code history elements stored into separate prefix

[codecov]

Codecov Report

Merging #317 (6027ded) into master (807956b) will increase coverage by 52.00%.
The diff coverage is 81.16%.

@@             Coverage Diff             @@
##           master     #317       +/-   ##
===========================================
+ Coverage   17.67%   69.68%   +52.00%     
===========================================
  Files          35       28        -7     
  Lines       10592     2388     -8204     
===========================================
- Hits         1872     1664      -208     
+ Misses       8606      606     -8000     
- Partials      114      118        +4     

Impacted Files	Coverage Δ
x/wasm/internal/types/types.go	23.52% <25.00%> (+1.90%)	⬆️
x/wasm/internal/types/keys.go	58.33% <63.63%> (+58.33%)	⬆️
x/wasm/internal/keeper/querier.go	50.99% <83.07%> (-0.44%)	⬇️
x/wasm/internal/keeper/legacy_querier.go	68.75% <93.54%> (+11.82%)	⬆️
x/wasm/internal/keeper/keeper.go	89.94% <100.00%> (-0.37%)	⬇️
x/wasm/internal/keeper/test_fuzz.go	94.11% <100.00%> (ø)
x/wasm/internal/types/genesis.pb.go
x/wasm/internal/types/msg.pb.go
x/wasm/internal/types/proposal.pb.go

[webmaster128]

Nice stuff; some thoughs