Refactor transaction storage pallet to use fungible traits (#1800)

Partial https://github.com/paritytech/polkadot-sdk/issues/226

`frame/transaction-storage`: replace `Currency` with `fungible::*`
traits

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Signed-off-by: Adrian Catangiu <adrian@parity.io>
Co-authored-by: georgepisaltu <52418509+georgepisaltu@users.noreply.github.com>