* add constructor for CheckOperator

* refactor the traits related to Currency

* format code

* modify

* update test cases

* update test cases

* update substrate

* fix tests

* Add dust removal and transfer_all in orml-tokens.

* Ensure existential rule for transfer, deposit and withdraw.

* orml-tokens transfer: return error if dest balance is zero and transfer amount below existential deposit.

* set_balance helper.

* Existential deposit unit tests.

* Fix orml-currencies mock.

* Renaming.

* Update transfer_all in orml-tokens.

* rename to FRAME

* fix test

* Rename paint to palette.

* Fix typo.

* Update comments.

* rename srml to paint

* fix case

* Tokens module: impl MultiCurrencyExtended.

* Minor fixes.

* Tokens module unit tests.

* Remove workspace src directory

* Add example crate.

* fmt

* Update example.

* Minor fixes.

* Remove allow dead code.