Re-org aggregationBits utils logic

[dapplion]

Motivation

Working on gossip validation I found the need to use this utils but the exposed API is not optimal.

Description

• Generalize the functions types and sames for CommitteeBits and SyncCommitteeBits
• De-duplicate code by exposing a single function that accepts TreeBacked and struct
• Expose convenience functions zipIndexesCommitteeBits, zipIndexesSyncCommitteeBits that already include the types

[codeclimate]

Code Climate has analyzed commit 945a46a and detected 1 issue on this pull request.

Here's the issue category breakdown:

Category	Count
Complexity	1

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