Fixing leaks in Mixxx

Most fixes are just freeing resources. std::vector does need more tricks to be surely it should be done this way: http://www.cplusplus.com/reference/vector/vector/clear/ (swap) not like it's done now with resize(0) (it works 90% times but not allways). Also share_ptr stuff make sometimes my hair fall.. Every commit have valgrind memory leak it's related.
Just read your commit comment -- deleteLater() actually deletes it once all pending events have been delivered, not at the end of the thread. Typically this happens on the next Qt event loop (so shortly after the call to deleteLater()).