Author: Juan Leyva
MDL-69555 tool_mobile: Allow to set QR login keys duration time
http://git.moodle.org/gw?p=moodle.git;a=commit;h=80a9eef971ed410dd02ab5266c44dbe9ab4af58f
http://github.com/moodle/moodle/commit/80a9eef971ed410dd02ab5266c44dbe9ab4af58f
+ 4.0 en [qrcodeformobileapploginabout,tool_mobile]
+ 4.0 en [qrkeyttl,tool_mobile]
+ 4.0 en [qrkeyttl_desc,tool_mobile]