Upgrade wasmvm aka go-cosmwasm

[alpe]

Resolves #309
This got a bit bigger than expected:

• Rename go-cosmwasm to wasmvm
• Upgrade wasmvm to `v0.12.0-alpha1
• Upgrade Dockerfile for new go-ext-builder
• Fix WasmConfig parsing
• New --wasm.lru_cache_size and --wasm.query_gas_limit wasmd start parameter
• Default "lru cache size" to 100 MiB
• Upgrade CircleCI build container to Go 1.15
• Stop tests on race conditions via GORACE=halt_on_error=1

[webmaster128]

Diff lgtm. Just one thing.

[codecov]

Codecov Report

Merging #311 (ac8437f) into master (cbda602) will increase coverage by 0.03%.
The diff coverage is 61.81%.

@@            Coverage Diff             @@
##           master     #311      +/-   ##
==========================================
+ Coverage   17.49%   17.53%   +0.03%     
==========================================
  Files          35       35              
  Lines       10505    10519      +14     
==========================================
+ Hits         1838     1844       +6     
- Misses       8566     8572       +6     
- Partials      101      103       +2     

Impacted Files	Coverage Δ
x/wasm/internal/keeper/api.go	60.00% <ø> (ø)
x/wasm/internal/keeper/handler_plugin.go	75.34% <ø> (ø)
x/wasm/internal/types/types.go	23.52% <0.00%> (-0.24%)	⬇️
x/wasm/module.go	22.00% <40.00%> (+7.71%)	⬆️
x/wasm/internal/keeper/query_plugins.go	74.55% <80.00%> (ø)
app/app.go	88.38% <100.00%> (-0.10%)	⬇️
x/wasm/internal/keeper/keeper.go	90.30% <100.00%> (+0.60%)	⬆️
x/wasm/internal/keeper/test_common.go	86.72% <100.00%> (ø)

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[alpe]

Pushed a new version

[webmaster128]

A bit more 💅 but looks nice overall

[ethanfrey]

Can you add these new command line flags to the README?

Otherwise, looks top.