Extensible transactions (and tips) (#3102)

* Make extrinsics extensible.

Also Remove old extrinsic types.

* Rest of mockup. Add tips.

* Fix some build issues

* Runtiem builds :)

* Substrate builds.

* Fix a doc test

* Compact encoding

* Extract out the era logic into an extension

* Weight Check signed extension. (#3115)

* Weight signed extension.

* Revert a bit + test for check era.

* Update Cargo.toml

* Update node/cli/src/factory_impl.rs

* Update node/executor/src/lib.rs

* Update node/executor/src/lib.rs

* Don't use len for weight - use data.

* Operational Transaction; second attempt (#3138)

* working poc added.

* some fixes.

* Update doc.

* Fix all tests + final logic.

* more refactoring.

* nits.

* System block limit in bytes.

* Silent the storage macro warnings.

* More logic more tests.

* Fix import.

* Refactor names.

* Fix build.

* Update srml/balances/src/lib.rs

* Final refactor.

* Bump transaction version

* Fix weight mult test.

* Fix more tests and improve doc.

* Bump.

* Make some tests work again.

* Fix subkey.

* Remove todos + bump.

* Ignore expensive test.

* Bump.