GenericAsset module (#2790)

* added generic asset module

* Update srml/generic-asset/Cargo.toml

* Update srml/generic-asset/Cargo.toml

* revert Cargo.lock changes

* cleanup line width

* rename srml_support to support

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* update comments

* more docs

* update Cargo.lock

* fix tests

* update headers and fix missing events

* Update srml/generic-asset/Cargo.toml

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update srml/generic-asset/src/lib.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* fix issues

* avoid duplicated code

* fix build issue

* cleanup Cargo.toml

* update based on reviews

* remove not used method

* update parity-codec version

* fix test build issue

* update Cargo.lock

* update with latest substrate changes

* refactor PermissionVersions encoding