Well, the repository window shows all files that are changed and not yet committed. The Journal also shows very clear the last commits in the current branch, but to see the committed files, you would have to use the Log and compare the HEAD with the commit of your choice. This won't work for uncommitted changes (ATM).

These are just colors to make reading the revision graph easier. Thin lines indicate unpushed commits. Note, that in Git a branch is just a named pointer to a commit. For a arbitrary commit you can't say in which branch it was created (as in Hg).

I recommend to take such topics to the mailing list.

So you just want a way to open the gitignore files of a selected repository? Maybe an external tool would solve this problem already?

How do you define "in this branch"?

For the repository context menu it would make sense (because it operates on the selection), but for the Files popup it does not operate on the context and won't be added there.