Add filter to `actions()`

[YaroShkvorets]

for the block.actions it shows all receiver actions (for token transfers that's 3x)

Well filtering the receiver seems like a very common thing, almost every single time

Seems like by default it should filter by receiver==contract and can be disabled as opt-in

Almost 100% everyone will hit this, expecting one action, but actually getting 3x and then trying to figure out how to filter it out afterwards

[YaroShkvorets]

• [x] actions() should always filter receiver == contract
• [x] add notifications() method that returns all actions where receiver != contract

[YaroShkvorets]

Done