Adds --no-validator CLI flag (#3348)

* Implement `is_validator` for offchain-workers

* Introduce `--no-validator` flag

* Don't run babe/grandpa/im-online when `--no-validator` is given

* Fixes compilation

* Bump spec version

* Improve error handling in executor

* Add missing extern function

* Revert making error public

* Remove `--no-validator` CLI

substrate/node/runtime/src/lib.rs

@@ -80,8 +80,8 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	// and set impl_version to equal spec_version. If only runtime
 	// implementation changes and behavior does not, then leave spec_version as
 	// is and increment impl_version.
-	spec_version: 136,
-	impl_version: 136,
+	spec_version: 137,
+	impl_version: 137,
 	apis: RUNTIME_API_VERSIONS,
 };