Allow for scanning single APKs
This MR factors out code for scanning a single APK into its own method. This allows projects using fdroidserver to scan individual APKs without needing to re-scan all APKs present in a repository.
Due to indentation changes, the diff is not very readable, but essentially code has just been moved around with the exception of
apkfile which is reconstructed in the
scan_apk() function and a
continue statement that is now done via a
skip return value.