Add DatabaseIndex

[renatomassaro]

Incidental

• Changed return type of build_file at the default ProcessView renderer for easier integration with the client
• Added bank_accounts information on the AccountIndex

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This change is 

[renatomassaro]

Reviewed 9 of 9 files at r1. Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable

[sourcelevel-bot[bot]]

Ebert has finished reviewing this Pull Request and has found:

• 1 fixed issue! 🎉

But beware that this branch is 2 commits behind the HackerExperience:master branch, and a review of an up to date branch would produce more accurate results.

You can see more details about this review at https://ebertapp.io/github/HackerExperience/Helix/pulls/393.