Fix require_once deprecation in syntax files

Fix warnings "Undefined variable" & "Undefined array key 1"

E_WARNING: Undefined variable $ID/../wiki/lib/plugins/popupviewer/syntax/viewer.php(62)
E_WARNING: Undefined array key 1/../wiki/lib/plugi

Fix warnings "Undefined variable" & "Undefined array key 1"

E_WARNING: Undefined variable $ID/../wiki/lib/plugins/popupviewer/syntax/viewer.php(62)
E_WARNING: Undefined array key 1/../wiki/lib/plugins/popupviewer/syntax/viewer.php(47)

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Check keepOpen with lower case.

fix #11

Add default class to popup link

Fixes #13 - the link can be used for additional styling information if required

Moved up some code

the Doku_HAndler_Parse_Media is only available during the handler phase.

Somehow Hogfather has a problem here.

Update tabs to spaces.

add metadata renderer

If the renderer has a `_media` function - as the default renderer has - use it.

fix relative media IDs

fix error third parameter missing

remove function call because it is called twice (there is onother one on line 109)

Adjust method signatures to match parent

Resolve ID so that relative IDs will work.

Add "keepOpen" option

Allows to keep the popupviewer open for links inside a popup.

avoid leading and trailing spaces on $more

Modify attributes to html5 valid data- ones

headers is now private API on DW renderer

Add implementation for image map

This allows to have popups inside the image map.

Add option to enable JavaScript in pages loaded by popupviewer.

Allow only one popupscript per page.

Add a popupscript tag that allows embedding script into a newly loaded page

This can only be done for direct popup pages, not links and it will run
the script in an inner scope.

Move syntax script for another syntax mode