rename "enable" action to "toggle"

The previous action caused confusion when it was called "enable" in the
WebUI for both a disabled and an enabled user. It created an expectation
that its name would change when the state of the user would change.

Fixes bug 1202187

Change-Id: I620843df730520b55bfb709aaff1d63ce3f6e772
Merge "rename "enable" action to "toggle""