Eresident only assets

[kacperzuk-neti]

First commit contains just vendoring-in pallet-assets, second commit contains actual changes.
DEX Liquidity Pool accounts are exempt from the eresidency restriction regardless the asset parameters set.

Known caveats:

1. If eresident owns restricted assets and puts them in dex, he can transfer liquidity tokens to non-eresidents. These non-eresidents won't be able to withdraw the liquidity to get actual restricted assets though.
2. Swaps on DEX can be triggered by non-eresidents as long as they set the immediate recipient of swap to valid eresident.

Sample guide on how to test:

1. Alice (citizen) - assets.create
2. Alice - assets.setParameters - eresidencyRequired: true
3. Alice - assets.mint to Alice
4. Alice - assets.transfer to Bob (citizen)
5. Alice - assets.transfer to Ferdie (non-citizen, should fail with TokenBlocked)
6. Alice - assetConversion.createPool with native
7. Alice - assetConversion.addLiquidity
8. Alice - assetConversion.swapTokensForExactTokens, swap Native to asset, should succeed
9. Ferdie - assetConversion.swapTokensForExactTokens, swap Native to asset, should fail with TokenBlocked