New database trait (#5549)

* Introduce trait

* The trait

* Generic

* Basic impls.

* Remove unneeded bounds

* Minor changes

* Switch over to the new DB trait

* Integrated parity-db and added CLI for db selection

* Default impl.

* Fix logs.

* Started integrating subdb

* Apply suggestions from code review

Co-Authored-By: Cecile Tonglet <cecile@parity.io>

* Apply suggestions from code review

Co-Authored-By: Nikolay Volf <nikvolf@gmail.com>

* Enable subdb

* Bump parity-db

* Fixed CLI macro

* Fixed browser build

* Fixed features

* Sort out features

* Use parity-db from crates.io

* Typo

Co-authored-by: arkpar <arkady.paronyan@gmail.com>
Co-authored-by: Cecile Tonglet <cecile@parity.io>
Co-authored-by: Nikolay Volf <nikvolf@gmail.com>

substrate/frame/support/src/traits.rs

@@ -208,7 +208,7 @@ pub trait Contains<T: Ord> {
 	///
 	/// **Should be used for benchmarking only!!!**
 	#[cfg(feature = "runtime-benchmarks")]
-	fn add(t: &T);
+	fn add(t: &T) { unimplemented!() }
 }
 
 /// Determiner to say whether a given account is unused.