Replace more instances new/delete with owning types (#4245)

* Use owning types when possible.

Note: the QByteArray s is detached to mimic previous behavior;
detach() guarantees that the QByteArray uniquely owns its data, since
otherwise it's COW. This may be relevant in case Plugin:instantiate
modifies s.data() -- this way the original QString is safe.

* Make m_filter a unique_ptr.

* Make m_activeRenderer a unique_ptr

* use std::string instead of strcpy + buffers

src/core/NotePlayHandle.cpp

@@ -53,7 +53,6 @@ NotePlayHandle::NotePlayHandle( InstrumentTrack* instrumentTrack,
 	PlayHandle( TypeNotePlayHandle, _offset ),
 	Note( n.length(), n.pos(), n.key(), n.getVolume(), n.getPanning(), n.detuning() ),
 	m_pluginData( NULL ),
-	m_filter( NULL ),
 	m_instrumentTrack( instrumentTrack ),
 	m_frames( 0 ),
 	m_totalFramesPlayed( 0 ),
@@ -155,8 +154,6 @@ NotePlayHandle::~NotePlayHandle()
 
 	m_subNotes.clear();
 
-	delete m_filter;
-
 	if( buffer() ) releaseBuffer();
 
 	unlock();