Major tasks undertaken in this patch:
* New format_text argument, overflowdiv.
* New page layout Report.
* Review of all format_text calls.
* Added support for the report layout to all themes.
* Changed forum post display from tables to divs.
* 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
