Bug 444545 - [validation] Ability to ignore custom html tag

Now it's able to ignore html element names from validation using comma-separated name patterns, that can be
specified on Validation Preference page, or set by a quick fix.

This is the Core only part of work that adds new preferences and makes Syntax Validator to use these new preferences.

Signed-off-by: vrubezhny <vrubezhny@exadel.com>