Adds support for storage parameter types (#6296)

* Adds support for storage parameter types

This pr adds a new parameter types type, the storage parameter types.
This parameter type supports loading the value from the storage or
returning the given default value.

* Use twox_128

* Update docs

* Update frame/support/src/lib.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>