Bugfix SUP-2110
When using the targetregex, cssclassregex and titleregex settings of the link plugin,
the corresponding attribute was not removed, when the current href did not match the
pattern. This has been fixed, and the behavior of this settings has been changed so
that the automatically set values will only be set, when the href of the currently
selected link changes, but not if another link is selected, which means that manual
changes to these attributes will be preserved, so long as the link href does not change.
Bugfix SUP-1041
The handling of <br> tags in empty paragraphs was consistent
across browsers. This has been fixed.