Improve Linkwizard, make it can be used more than once.

As reported in https://forum.dokuwiki.org/thread/9988
the previous implementation can not handle the situation of use the
linkwiz more than once. Now you can use in you toolbar plugin
    'type' => 'linkwiz'
to make use of the handy Linkwizard for choosing the wiki pages.
Merge pull request #235 from haobug/master

Improve Linkwizard, make it can be used more than once