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/sr-primitives/src/lib.rs

@@ -266,6 +266,21 @@ impl From<H512> for Ed25519Signature {
 	}
 }
 
+/// Context for executing a call into the runtime.
+#[derive(Copy, Clone, Eq, PartialEq, Encode, Decode)]
+#[cfg_attr(feature = "std", derive(Debug, Serialize))]
+#[repr(u8)]
+pub enum ExecutionContext {
+	/// Context for general importing (including own blocks).
+	Importing,
+	/// Context used when syncing the blockchain.
+	Syncing,
+	/// Context used for block construction.
+	BlockConstruction,
+	/// Context used for other calls.
+	Other,
+}
+
 #[derive(Eq, PartialEq, Clone, Copy, Decode)]
 #[cfg_attr(feature = "std", derive(Debug, Serialize))]
 #[repr(u8)]