[TIDY] Refactor renderlib into two parts

Most of the make scripts only need the schedule part of the renderlib.
The schedule part has way less dependencies (e.g. no ImageMagick), so
those scripts can be used without them now.

make-blender.py

@@ -7,7 +7,7 @@ The blender project must be configured to use mkv/matroska as output file format
 """
 
 import subprocess
-import renderlib
+import schedulelib
 import argparse
 import tempfile
 import shlex
@@ -147,7 +147,7 @@ elif args.bgloop:
     }]
 
 else:
-    events = list(renderlib.events(args.schedule))
+    events = list(schedulelib.events(args.schedule))
 
 
 def describe_event(event):