Redesigned FileAnalyzer and Analyzer task. New design is much cleaner, resulting...

Redesigned FileAnalyzer and Analyzer task. New design is much cleaner, resulting in simpler code and faster file import performance. Also, playlist files are now handled ahead of everything else, which makes sure the progress indicator increases monotonically. Preliminary tests show that file import performance has been more than doubled! For example, the time for importing ~1000 files decreased from 116 seconds to 46 seconds on the development machine, which corresponds to a 2.5x speed-up.