Replace CRC32 with Another Hash Function

[DavidBerdik]

InfiniDrive currently makes use of the CRC32 hash function to validate the integrity of uploaded fragments. With the introduction of the update command, the values produced by this hash function are now used to determine if two fragments are identical. This is potentially risky, as CRC32 has a collision rate that is higher than other hash functions. It would be worth looking in to replacing CRC32 with a hash function that is less prone to collision. Obvious candidates are MD5 and SHA256.

[DavidBerdik]

The decision was made to add SHA256 support in addition to CRC32. By using two hashes, we should be safe from collisions. SHA256 support was introduced in 7994b44.