Implement end-to-end correctness and performance tests.

[Antzen]

Develop comprehensive tests and benchmarks for the file mutability feature. Also include some accompanying sanity checks in the form of unit tests.

[rzhang0720]

Anant and I have created a document outlining test use cases and procedures:
File Appends Testing Outline

[rzhang0720]

Development for this task has begun on the test/file-append branch.

[anant12]

Link to branch commits: https://github.com/comp413-2017/RDFS/commits/test/file-append.