Resolve user alias for asset methods (balances, transfer etc.)

[dzikowski]

Currently UserProfile is saved on GCUP/<eth-addr> key and contains the alias field. When you authorize with signature-based auth ctx.callingUser is set to alias. Also all balances and other user-related key parts use alias. But when you do some operations, like fetching balances or tranferring tokens, we don't search for aliases. If you provide eth|<ath-addr> for user that has an alias, it won't find the alias, which leads to potentially inconsistent state.

Implementation proposal:

1. For all DTO parameters which point to user, use a custom class UserId (like owner?: UserId in FetchBalances)
2. UserId should be serialized to string and deserialized from string to something like { "userId": string }
3. For all ChainObject parameters which point to user, use a custom class - UserAlias.
4. UserAlias should be serialized to string containing user alias to keep backward compatibility (we use alias-first approach), and deserialized to something like { "alias": string }.
5. Each time you want to use UserAlias type, you need to get it with some custom method like getUserAlias(id: UserId): UserAlias. This way we keep type-safety and enforce resolving user aliases.

Additionally we should support lower-cased eth addresses (not only checksumed ones)

To be considered:

1. Maybe we should implement it once we drop the legacy auth: Drop support for legacy auth #176 There is a risk that making it backward compatible with the legacy auth may be problematic. But there is also a benefit of making it backward compatible - no need to wait till the 2.0 release.