Upgrade allocation payer-based logic

[andrenerd]

Cleanup and extend logic related to Allocation.PayerID field. Don't mess it with Read/WriteMarker.PayerID, they have different "nature".
The changes supposed to be used to implement freeStorage feature later too.

List of possible changes:

• Drop some legacy Allocation.PayerID-linked logic, that was used by "Repair" features that were completely removed.
  31339e9

• Make Allocation.PayerID independent value, that, if provided, should indicate, that all operations for the Allocation are payed by this payer by default.

• The could be implemented exceptions, only if another Payer explicitly indicated. for example, by "rx_pay" flag. It's could be important to note, that Allocation.PayerID is not de-facto used for "rx-pay" logic, even though a comment in the current Allocation struct declaration tells that!

Outcomes:
The changes let to set PayerID value on allocation creation for the freeStorage scenario. The value could set to Owner. Or possibly another user, if it will be required by new use cases.

[andrenerd]

Notes for the future:

• former "misused" PayerID moved to RepairerID.
• RepairerID is used for access checking and has nothing with payments or PayerID.
• RepairerID has been used to store value for (blobber?) node id. It's not client id. Don't be confused by the legacy code.

[guruhubb]

@MurashovVen please comment on the repair flow, because you were working on the add/drop blobber and we need to make sure the changes do not affect your PR later.

[MurashovVen]

I have not started the implementation of add/drop function, so there should be no conflicts here.