Add ability to set storage engine for library

[Floppy]

Filesystem only at the moment, so no actual useful change for users here.

[qlty-cloud-legacy[bot]]

Code Climate has analyzed commit 4c0cd154 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 83.3% (50% is the threshold).

This pull request will bring the total coverage in the repository to 85.6% (0.0% change).

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