Define Zeno's queuing behavior properly

[CorentinB]

As discussed with @equals215, Zeno's behavior in term of queuing should be as followed:

• By default: handover + WAL writes batching
• As an option: --disable-handover, --whatever (--whatever == a good argument name to ask for more atomicity == not use WAL batch writing)
• When using HQ: handover++ (no queuing AT ALL)

[equals215]

Options and defaults can be done in under a minute. Handover++ as you call it, can either be done on the fly or integrated to #113 in the channeling efforts, as you wish @CorentinB

[CorentinB]

I guess it should be integrated in #113.