Effect class name is used when introspecting the available effects
for a given build of libopenshot, for example when extracting
translation strings for OpenShot. The EffectInfo::class_name member
needs to match the name of the class it describes, which two of ours
did not.
- ObjectDetection had its class name set to "Object Detector", which
obviously isn't the class name.
- Tracker, worse, was allowing class_name to be **SET** from the
JSON parameters passed to its SetJSON() method, making the class
name mutable at the whim of the class's callers.
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