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/client/src/runtime_api.rs

@@ -25,7 +25,7 @@ pub use primitives::NativeOrEncoded;
 #[doc(hidden)]
 pub use runtime_primitives::{
 	traits::{AuthorityIdFor, Block as BlockT, GetNodeBlockType, GetRuntimeBlockType, ApiRef, RuntimeApiInfo},
-	generic::BlockId, transaction_validity::TransactionValidity
+	generic::BlockId, transaction_validity::TransactionValidity, ExecutionContext,
 };
 #[doc(hidden)]
 pub use runtime_version::{ApiId, RuntimeVersion, ApisVec, create_apis_vec};
@@ -99,6 +99,7 @@ pub trait CallRuntimeAt<Block: BlockT> {
 		changes: &mut OverlayedChanges,
 		initialised_block: &mut Option<BlockId<Block>>,
 		native_call: Option<NC>,
+		context: ExecutionContext
 	) -> error::Result<NativeOrEncoded<R>>;
 
 	/// Returns the runtime version at the given block.