Makes the fork activation to happen exactly on the defined block number.

Fixes tests to support legacy TXs.

Adds Gas and GasPrice validation to consensus.

Fix 1894465465 to release process... uppercase readme.

Build only linux binaries because of a cross-compilation hell with cr…

…ypto C libs.

Removes 386 compilation binaries from release bc of:

```
gopkg.in/olebedev/go-duktape.v3
# gopkg.in/olebedev/go-duktape.v3
../../../../pkg/mod/gopkg.in/olebedev/[email protected]/dbgsockettransport.go:14:16: undefined: Context
../../../../pkg/mod/gopkg.in/olebedev/[email protected]/dbgsockettransport.go:16:15: undefined: DebugRequestFunc
../../../../pkg/mod/gopkg.in/olebedev/[email protected]/dbgsockettransport.go:17:15: undefined: DebugDetachedFunc
```

status-im/status-go#1793 (comment)

Cleans installation process (no more ducktape warnings).

Fixes race failure in TestNode_MiningSpamTransactions.

Fixes race condition in TestNode_MiningSpamTransactions.

Makes tests faster by using smaller mining difficulty.