Stabilize 0-db

[rkhamis]

We will need anytime soon a full stable 0-db version, with compaction (and replication, if possible) working as expected, to avoid disk overflow during grid launch.

I'll work on theses issues at first:

• Make 0-db a reusable library threefoldtech/0-db#43
• Clean tools code and avoid code copy threefoldtech/0-db#44
• Compaction tools threefoldtech/0-db#35

Then on theses one:

• Implement everything needed for replication threefoldtech/0-db#53
• db-replicate isn't working as expected threefoldtech/0-db#59
• db-mirror isn't working as expected threefoldtech/0-db#60