renamed Visible to Availability and added help strings
AMOS BEGIN
CPY [availability,core_moodle],[modvisible,core_moodle]
CPY [availability,core_moodle],[modvisiblewithstealth,core_moodle]
CPY [availability,core_moodle],[modvisiblehiddensection,core_moodle]
CPY [show,core_moodle],[modshow,core_moodle]
CPY [hide,core_moodle],[modhide,core_moodle]
AMOS END
It should be possible for activities to be visible even when the section
they are in is hidden.
However, when a section is hidden, all activities in that section are also
then initially hidden. Therefore, this commit splits out the hidden test to
a new test so that the initial state of activities after hiding can still
be tested.