timeline: heavily optimized and improved nearly all timeline optimizations

Features a lot of timeline-related cache optimizations as well as general
optimizations and improvements in timeline behavior. Should improve
usability significantly.

app/node/block/clip/clip.cpp

@@ -62,7 +62,7 @@ NodeInput *ClipBlock::texture_input() const
 void ClipBlock::InvalidateCache(const TimeRange &range, NodeInput *from, NodeInput *source)
 {
   // If signal is from texture input, transform all times from media time to sequence time
-  if (from == texture_input_) {
+  if (from == texture_input_ || from == media_in_input()) {
     rational start = MediaToSequenceTime(range.in());
     rational end = MediaToSequenceTime(range.out());