In Branches pane, show count of branches in each subpath

Currently, the "Branches" pane shows a count of the number of branches in each top-level group (e.g. "Local Branches (3)" or "origin (27)"). And when "Group tags and branches by path-like name" is selected, there's a sub-group for each initial path component, with all branches having the same path component underneath that group.

Problem: we use path grouping for different developers, and some developers have gotten out of control on how many of their branches are still hanging around. But, it's hard to see which developer has lots of branches and which has few.

Suggestion: have the sub-groups display the count of branches within that sub-group.