Add clips to tracks and tracks to track containers only after the constructor completes

[sakertooth]

Currently, we add tracks and clips prematurely to there respective containers, i.e., they are added within the base class. This has seemed to have caused a number of problems involving calls to pure virtual functions (because the object wasn't fully created yet), to dynamic_cast failures and ultimately crashes. This PR fixes this by only adding a track or clip to their respective containers after the object has been fully constructed.

[Rossmaxx]

A few thoughts. Another doubt I have is that, does this fix that crash with deleting a track while playing?

[sakertooth]

A few thoughts. Another doubt I have is that, does this fix that crash with deleting a track while playing?

I believe crashes like those happen because of synchronization issues involving mutexes (which I believe should be fixed, albeit not ideally). What I am addressing here with this PR is the problem where we are adding clips to tracks and tracks to track containers (like the song editor) way too early. If I created a SampleTrack object for example, it would add itself to the song editor when its constructor hasn't completed yet. This has caused a number of bugs when processing the Song.

[sakertooth]

A few thoughts. Another doubt I have is that, does this fix that crash with deleting a track while playing?

Wow, I discovered something. When tracks are deleted, only the base destructor is called (Track::~Track) and not the derived one (maybe something like SampleTrack::~SampleTrack for example) because the destructor isn't virtual. Destructors like SampleTrack::~SampleTrack remove all play handles associated with that track, but it may not be ran when deleting it at all. I'm just realizing how many issues need to be fixed here.

Wait, nevermind, whatever Track inherits have virtual destructors already. I do remember that we covered these cases with a clang-tidy PR awhile back actually.

[sakertooth]

PR too big. Started over. This PR is only concerned with delaying the addition of clips to tracks and tracks to track containers after the constructor is complete.