NEP-17 tracker tracks NEP-11 events

[roman-khimov]

Describe the bug
NEP-17 tracker code checks for Transfer events and records data from them into its storage. The problem is that in its current form it can easily catch NEP-11 event and treat it as NEP-17 event, it'll be stored and used for answering RPC requests (getnep17transfers/getnep17balances).

Expected behavior
NEP-17 tracker should only track NEP-17 events.

Potential solutions
neo-project/neo#1883