Changing branch owner unintuitive

[Mackenzie Morgan]

When looking at a branch, there are two options on the right sidebar. One is "change branch details", and the other is "change branch reviewer." Since in other places on Launchpad (like, say, for projects) choosing to change the maintainer lets you change both that and the driver, I thought maybe when I clicked on reviewer that that'd let me change owner. Nope.

2 people and 30 minutes later, we figured out:
- changing reviewer doesn't actually give people in the reviewer team access to push (confusing)
- that the "change branch details" link includes the part to change the owner

Also confusing:
The part where you can change the owner doesn't tell you that it'll change the path for the branch. I was unsure whether "change owner" was what I wanted since I didn't know if it'd change the path and permissions (what I wanted) or just the permissions (what I didn't want), so some text saying what it does may help.