* 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
There are multiple issues with Moodle files containing empty or blank lines
(lines consisting of white spaces or tabs only) and/or white space before or
after the PHP open and close tags, notably with config.php and theme files.
* in_null for decimals defaults checks
* store letter settings only in database - no cfg settings
* separate configuration page for letters only - pluginselector+admin tree
* new capability to manage grade letters - similar to scales and outcomes
* added grade_letters db index
* grade letters related minor bugfixing
