Add support for destroying assets

[annatekl]

The Objective of this ticket is to add a mechanism for destroying or unclaiming the ownership of an asset.

Requirements

When destroying an asset, the balances of this asset should get removed from all accounts holding it and it should be possible for a new user to claim ownership of this asset again. Upon destruction, the initial deposit for claiming ownership is transferred back to the depositor.

[ebma]

I updated the description.