Review and fix management of lifetime for core animation instances

Since Qt 5.0 there have been a number of commits fixing crashes in the internal QML animation classes (those in src/qml/animation):

• 11e9c49e5420bf749e4da48b1f14fa7dc9e4716f
• 114c9a16e240558a8aea2004696369e78ef5ac80
• ad821a63bf4075f2b18ec9eaa6d58f8fd721269a
• https://codereview.qt-project.org/38796
• https://codereview.qt-project.org/81973

These fixes generally consist of wrapping function calls that are somehow "accessible" to QML with RETURN_IF_DELETED. There are likely further instances where crashes are possible. The code should be reviewed, and:

• all applicable function calls be wrapped with RETURN_IF_DELETED (and RETURN_IF_DELETED possibly optimized?), or
• a new strategy for lifetime management used (so these classes are never deleted in a way that could crash; e.g. something like deleteLater?)