Prevent opening several times the same documentation

When the user clicks on a documentation button, the documentation may take some time to appear, letting the user clicking several other times on the button and resulting in several documentation windows. After one click on the button, there should be a spinner displayed and the button should be insensitive until the documentation as actually displayed (or closed?)

Parent Task: #10828 (closed)

Original created by @alant on 11325 (Redmine)