Author: Marcus Green
MDL-58248 theme_boost: label/span for sidepanel expand button
Add string "Side panel" to make the purpose of
trigram/hamburger icon at top left clearer, particularly
when using screen readers e.g. Jaws/NVDA.
Currently it reads out only "expand"
http://git.moodle.org/gw?p=moodle.git;a=commit;h=78af4ba0532eed2866e2223eb1baead860862d93
http://github.com/moodle/moodle/commit/78af4ba0532eed2866e2223eb1baead860862d93
+ 3.4 en [sidepanel,core]