Show full submodule changes in Local Changes

[davidfraser]

When committing an update to a submodule, SourceGit shows
SUBMODULE
Current Commit Info
(down arrow)
NEW COMMIT
This shows what will change in the commit.
However, it would be useful to be able to see a lot more information:

• What files within the submodule would change (similar to the diff view shown when selecting two commits in the History/Graph view)
• What git commits are being introduced? (git gui shows this as the diff, showing new commits with >). Some kind of tree view could also work here.
  A button that says "Show Submodule Change" which switches to the graph view for the submodule with the two commits selected would have the effect of showing all the required information