Issue #46: add callbacks for modifying a form

[dmitriim]

This pull requests adds following callbacks to let other plugins to extend edit dates form the same way as they can extend core moodle activity forms:

• report_editdates_form_elements
• report_editdates_form_definition_after_data
• report_editdates_form_validation
• report_editdates_form_post_actions

This is required, if for example some customisation has been been applied to an activity form to manipulate dates fields (e.g. to limit a possible time options for an assignment due date) and we would like to apply the same customisation to edit dates form to make sure that academics receive a consistent experience.

[cameron1729]

Thanks @dmitriim - these changes make sense to me. I looked at them in tandum with catalyst/moodle-local_submissionrestrict#3 which helped to give me some context for the how the hooks are intended to be used. Code gets my +1

[timhunt]

So, err, you have done something. Apparently, if, like Cameron, I go and read some other code, I might be able to work out what you aren doing and why.

Or, here is an idea. If you are proposing a change in some code, why don't you explain what you are doing, and why, then I will review it.

So far, it seems like you know exactly what you are doing and why, and you think you have explained it, but really you have not. So, please try to actually explain.

[dmitriim]

@timhunt I have added more information to the description of the pull request. Hope it makes more sense now.