Merge branch 'install_28_STABLE' of https://git.in.moodle.com/amosbot/moodle-install into MOODLE_28_STABLE

    Also unit tests were added to cover the new clean_data() method.

    Also the get_property_definition() was created to get the property without retrieve the whole definition cache and
    unit tests were created to tests those new methods.

Thank you to Zachary Durber for originally working on this issue.

When getting the navigation branch data through AJAX, require
login if forcelogin is set.

Singleview users must have Manage Grade permission to modify the
Exclude grade attribute.

This issue mostly affects the search form fields. Submitted values for
these fields are typically obtained via optional_param() with
PARAM_NOTAGS specified as the parameter type - see parse_search_field()
methods. Such values themselves are not safe enough to be printed back
directly into the HTML as they might contain malicious code.

While working on the patch, some other places with weak protection were
detected and fixed.

In case of the itemid parameters, the s() seems to be unnecessary but it
was added anyway as an extra protection (just in case the code flow
changes or the parts of the code are re-used elsewhere).

Merge branch 'install_28_STABLE' of https://git.in.moodle.com/amosbot/moodle-install into MOODLE_28_STABLE

Only important change is that Moodle 2.7 installed is
required to be able to upgrade to 3.1. See the issue
for opinions, votes and agreed outcomes.

Merge branch 'install_28_STABLE' of https://git.in.moodle.com/amosbot/moodle-install into MOODLE_28_STABLE