DRAFT: deposits pallet DONT MERGE

[trusch]

This is not meant to be merged. It only serves as a playground for ideas and will be completely rewritten once we consolidated our thoughts on it.

fixes KILTProtocol/ticket#312

Please include a summary of the changes provided with this pull request and which issue has been fixed. Please also provide some context if necessary.

How to test:

Please provide a brief step-by-step instruction. If necessary provide information about dependencies (specific configuration, branches, database dumps, etc.)

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Checklist:

• [ ] I have verified that the code works
  • [ ] No panics! (checked arithmetic ops, no indexing array[3] use get(3), ...)
• [ ] I have verified that the code is easy to understand
  • [ ] If not, I have left a well-balanced amount of inline comments
• [ ] I have left the code in a better state
• [ ] I have documented the changes (where applicable)