Split handle results returned in AtomDB queries into different slots

[andre-senna]

Initially we'll have two policies to create slots:

• Sort all results by importance and slice the sorted list into slots i.e. given m slots of size n, slot 1 will contain the first n/m handles. slot 2 will contain the next n/m handles etc.
• Sort all results by importance and distribute the most important ones among each slot i.e. given m slots of size n, the first handle goes into slot 1, the second goes into slot 2, etc... until slot m. Then we rotate putting handle m+1 again in slot 1, m+2 in slot 2 etc.