Merge pull request #8 from bennettslin/master

fix redo for both delete and load new files, then add mixIn1 button to xib
Merge pull request #9 from bennettslin/master

connect undo and redo menu items to their methods
small changes to seek slider
Merge pull request #10 from yairsz/YairsWorkBranch

small changes to seek slider
Merge remote-tracking branch 'upstream/master'
move audio mix concerns to tap processor