srml-module: Phragmen election (#3364)

* phragmen election module.

* Add new files.

* Some doc update

* Update weights.

* bump and a few nits.

* Performance improvement.

* Master.into()

* Update srml/elections-phragmen/src/lib.rs

Co-Authored-By: Gavin Wood <[email protected]>

* Fix build

* Some fixes.

* Fix build.

* Proper outgoing and runner-up managment.

* Bit more sensical weight values.

* Update srml/elections-phragmen/src/lib.rs

* Update srml/elections-phragmen/src/lib.rs

Co-Authored-By: Gavin Wood <[email protected]>

* Update srml/elections-phragmen/src/lib.rs

Co-Authored-By: Gavin Wood <[email protected]>

* Update srml/elections-phragmen/src/lib.rs

Co-Authored-By: Gavin Wood <[email protected]>

* fix lock file

* Fix build.

* Remove runner-ups

* Some refactors.

* Add support for reporting voters.

* Fix member check.

* Remove equlize.rs

* Update srml/elections-phragmen/src/lib.rs

* Update srml/elections-phragmen/src/lib.rs

* Update srml/elections-phragmen/src/lib.rs

Co-Authored-By: Gavin Wood <[email protected]>

* Update srml/elections-phragmen/src/lib.rs

Co-Authored-By: Gavin Wood <[email protected]>

* Bring back runner ups.

* use decode_len

* Better weight values.

* Update bogus doc

* Bump.

* Update srml/elections-phragmen/src/lib.rs

Co-Authored-By: Gavin Wood <[email protected]>

* Review comments.

* One more test

* Fix tests

* Fix build

* .. and fix benchmarks.

* Update srml/elections-phragmen/src/lib.rs

* Version bump