Large commit diff view load slow block main thread, better manual trigger load

A commit may add or modify many many files with a lot of diffs.
When click on a commit from History or Search view, bottom right window will try to load all the diffs of this commit. (tree view, defaults select the top folder)
This make SourceTree not response for a really long time.

See demo video in attachment for more detail.
Try the demo project to experience for yourself.