Adds new execution strategy nativeElseWasm (#1546)

* fix: adds new execution strategy nativeElseWasm and replace nativeWhenPossible with it

* feat: adds cmd line params for execution strategies

* fix: uses of cmd line execution strategies

* chore: remove white spaces

* chore: remove println

* chore: remove whitespace

* fix: generating functions with context

* feat: add function to generate with_context declarations

* fix: add implementation for with_context function calls

* fix: add execution context to call_api_at function

* fix: making use of context to select strategy for block_builder

* chore: cleaning up

* fix: merging issues

* fix tests

* add wasm files

* chore: small doc for context fields

* chore: delete redundant docs

* fix: use full path for ExecutionContext

* fix: add context functions from inside fold_item_impl

* chore: remove clone

* fix: moving generative function to utils, remove unused imports

* fix: add missing full path for ExecutionContext

* fix: merge issues

* update wasm files

* fix: update to keep up with changes in master

* chore: remove unused functions, clean up

* fix test

* fix grumbles

* fix: add more tests

* fix: some refactorings

* feat: add execution strategy to call

* chore: small improvements

* fix: add message to panic

* fix tests

substrate/core/rpc/src/state/mod.rs

@@ -35,6 +35,7 @@ use crate::rpc::futures::{stream, Future, Sink, Stream};
 use runtime_primitives::generic::BlockId;
 use runtime_primitives::traits::{Block as BlockT, Header, ProvideRuntimeApi, As, NumberFor};
 use runtime_version::RuntimeVersion;
+use state_machine::ExecutionStrategy;
 
 use crate::subscriptions::Subscriptions;
 
@@ -297,7 +298,7 @@ impl<B, E, Block, RA> StateApi<Block::Hash> for State<B, E, Block, RA> where
 			.executor()
 			.call(
 				&BlockId::Hash(block),
-				&method, &data.0
+				&method, &data.0, ExecutionStrategy::NativeElseWasm
 			)?;
 		Ok(Bytes(return_data))
 	}