This commit:
a) moves modinfo code into new library modinfolib.php
b) uses classes instead of stdClass objects, allowing a huge amount of documentation (and IDE completion)
c) adds hooks so that plugins other than forum can display messages like forum's 'unread', and plugins other than label can display html (apart from/as well as their view.php link) on the course view page
d) removes current hacks for forum and label (mainly in print_section but also across the code), replacing with new 'content' and similar variables [this is the reason for the changes in blocks, etc]
e) reduces size of modinfo in database (only when rebuilt) by excluding empty fields
The change is intended to be backward compatible and does not affect the format of modinfo in database.
* class html_component does not exist any more
* class html_table rendered via html_writer::table()
* html_table, html_table_row and html_table_cell have public $attributes property to set their CSS classes
* dropped rotateheaders feature, should be added again after more research of possible ways (<svg> is not nice IMHO)
* dropped possibility to define CSS classes for table heading, body and footer - can be easily done and better done using just table class and context
