Fix indentations.
Remove aliasing in header.
Use inner app pointer in VkMusicCache instead VkService::app()
Put all the methods above the data members.
Rename kDefCacheDir() to DefaultCacheDir() and use Utilities::Path_CacheRoot instead home dir.
Add missing const
Fix some whitespace style issues.
Remove usless comments
Replace QUrl::toString() to scheme(), host() and path() using.
Add set_valid() to Song conversion functions.
Fix typo, misspelling and odd naming.