Add oshash support

[WithoutPants]

Adds an oshash column to the database and makes checksum nullable. Added check to the scenes table to ensure at least one of the two are not null.

Introduces two new settings calculateMD5 and useMD5.

calculateMD5 indicates whether or not to calculate the MD5 checksum during scanning. oshash will always be calculated for scenes where it is not already present. Similarly, if calculateMD5 is true and the checksum is empty, then the MD5 will be calculated.

useMD5 indicates whether to use the MD5 checksum or the oshash for generated file naming and import/export naming.

For existing systems, these settings are both defaulted to true after migration if the scene table is not empty.

New systems have calculateMD5 and useMD5 set to false.

The system prevents changing useMD5 to false if there are any missing oshash values. Similarly, changing useMD5 to true will be prevented if there are any scenes without checksums. Finally, calculateMD5 is prevented from being set to false if useMD5 is true.

Adds hash to the file info panel in the UI. Missing hashes are not displayed.

Adds a manual migration task that renames existing generated files (not including exported metadata files) to the current naming format.

The oshash algorithm has been verified manually using the sample files from the opensubtitles website.

Resolves #351

[WithoutPants]

I think it's probably worth extending this to include galleries as well.

[bnkai]

My only concern for galleries would be how unique the hash is if we use zip files or files that can be <64k ( small zip file with a single image, or plain image in the future). I think it was mainly tested with video files.

[WithoutPants]

Yeah, you're right. Might be better leaving it off.

[bnkai]

It seems to work ok (excluding the sprite image renaming) both with an empty/existing db.
Initial oshash scan for my existing ~4TB, 11K scenes (stored on local HDDs) took ~6 minutes.
The name migration took < 5s ( nvme ssd)

[WithoutPants]

Merged in from develop branch. There was quite a bit of conflicting changes, so may need a retest.

Fixed up the logging and status stuff identified. Also fixed a nasty panic when running clean if a file is not accessible.

[bnkai]

Retested seems ok.

[bnkai]

I finished retesting. It wasnt an exhaustive test though, more of a check for regressions due to refactoring test. Looks ok.

For users with existing databases i think a step by step migration guide could be useful.
Eg.

1. Scan library ( updates the oshash for existing entries)
2. Untick UseMD5
3. Choose oshash as the naming scheme
4. Migrate