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.
Hm, no you're absolutely right -- sorry about that. deleteLater won't work here since the BeatGrid / BeatMaps have no parent so they live in the thread that created them (the main thread for tracks that already have beat data in the library and the analyzer thread for beatgrids detected this session).