Implement PSP34 standard

[realnimish]

Closes #6

[realnimish]

I've added the support of PSP34 & PSP34Metadata standard so far.
ArtZero integration expects a lot more traits, namely - Ownable, PSP34Enumerable, Psp34Traits, AdminTrait.

Issues:

1. PSP34Enumberable expects support of iterating over all NFTs.
2. Not sure what's AdminTrait::transfer_psp22. Asked on the telegram.
3. Psp34Traits is very rigid - messages with a problem -
   • token_uri expects token_id: u64 as input
   • get_last_token_id is meaningless in our case at the moment.
   • lock metadata

[wottpal]

Looks good so far, most points I highlighted are naming/consistency-related.

When I run the tests locally I get the following warnings, you might want to fix this, too:

warning: unused variable: `operator`
    --> azns_registry/lib.rs:1008:13
     |
1008 |             operator: &AccountId,
     |             ^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_operator`
     |
     = note: `#[warn(unused_variables)]` on by default

warning: unused variable: `from`
    --> azns_registry/lib.rs:1009:13
     |
1009 |             from: &AccountId,
     |             ^^^^ help: if this is intentional, prefix it with an underscore: `_from`

warning: unused variable: `to`
    --> azns_registry/lib.rs:1010:13
     |
1010 |             to: &AccountId,
     |             ^^ help: if this is intentional, prefix it with an underscore: `_to`

warning: unused variable: `id`
    --> azns_registry/lib.rs:1011:13
     |
1011 |             id: &Id,
     |             ^^ help: if this is intentional, prefix it with an underscore: `_id`

warning: unused variable: `data`
    --> azns_registry/lib.rs:1012:13
     |
1012 |             data: &Vec<u8>,
     |             ^^^^ help: if this is intentional, prefix it with an underscore: `_data`