Audit 0.2.1

[marco-sundsk]

Ref exchange audit

1. MAX_ACCOUNT_LENGTH is incorrect -- fixed;
2. u128 can not be correctly serialized -- fixed;
3. execute_actions should verify actions number -- reject to enable nope action;
4. execute_actions is not payable -- fixed;
5. Wrong error code in execute_actions -- fixed;
6. parse_token_id logic may cause problem. -- fixed;

   using :nn as a partern of pool lpt token

7. mft_transfer may cause problem. -- fixed;
8. Use different spec for MFT -- fixed;
9. migrate is not private -- fixed;
10. Simple pool can be created with 0 tokens. -- fixed;
11. LookupMap shares prefix issue -- fixed with StorageKey;
12. Ability to drain the pool without paying using instant swap. -- fixed;
13. Never unregister a LP when he remove liqudity.
14. shutdown instant swap from the interface;