feat(runtime): Adding dust and slash handlers

[ekovalev]

• Dust and slashes handlers to pallets configs to keep the total issuance consistent
• Tests

[breathx]

Seems all holes for leak of total issuance solved so we are able to introduce migrations with burning token from offset pool to stabilise issuance?

[NikVolf]

Seems all holes for leak of total issuance solved so we are able to introduce migrations with burning token from offset pool to stabilise issuance?

this is better be done via referendum

[ekovalev]

Seems all holes for leak of total issuance solved so we are able to introduce migrations with burning token from offset pool to stabilise issuance?

Seems so. The slash handlers called by other pallets (like bounty and child-bounty) implicitly call the same Treasury::OnSlash(). In all other places we are already handling the imbalances.