Move test crates into a "testing" folder and add a ui (trybuild) test and ui-test helpers (#567)

* move test crates into a testing folder and add a ui test and helpers

* undo wee mixup with another PR

* cargo fmt

* clippy

* tidy ui-tests a little

* test different DispatchError types

* refactor dispatch error stuff

* name ui tests

* duff => useless

* align versions and cargo fmt

testing/test-runtime/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "test-runtime"
+version = "0.21.0"
+edition = "2021"
+
+[dependencies]
+subxt = { path = "../../subxt" }
+sp-runtime = "6.0.0"
+codec = { package = "parity-scale-codec", version = "3.0.0", default-features = false, features = ["derive", "full", "bit-vec"] }
+
+[build-dependencies]
+subxt = { path = "../../subxt" }
+sp-core = "6.0.0"
+tokio = { version = "1.8", features = ["macros", "rt-multi-thread"] }
+which = "4.2.2"