Split Verify Signature from Verify Checksums

[szmarczak]

Describe Your Suggestion

VPK signature (if present) and file-wide MD5 checksums are now properly checked in the "Verify Checksums" tool

I don't want to verify checksums because it takes ages to verify them, hence delaying the information whether the signature is present. Optionally, add a new entry in the menu to verify just the signature.