extra_html_tag_attribute feature

[haricot]

This is like extra_css_classes and extra_inline_style with a little difference in setting format.
The Class HmltAttrsWidget has pre-set widget which can be entered in the settings file:
widget_choices_cms_page_anchors, widget_choices_list, widget_choices_int, widget_choices_text, widget_choices_color, widget_attrs.

( NAME_SERIE_ATTRIBUTES, {
     ATTRIBUTE: {
        PRESET: [] ,
        'widget_attrs': { 'title': TEXT },
     },
 })

Look like:

Todo: add the test if this feature is ok or need modifications.

[haricot]

closed in favor of #363