Makup leggero-v2 theme

[Fraenkiman]

This elevates the Leggero-v2 style to a more modern design. In most situations in life, first impressions count. The FlatPress Leggero-v2 style is what the user sees first after performing the setup. Potential new users may not immediately find their way to the wiki to see the variety of themes there - and hastily delete FlatPress again. Therefore I made a few small changes to the style:

• Adjusted the alignment of the calendar widget and the search widget.
• A single PhotoSwipe image or a whole gallery is now centered in the responsive design. #150
• BBcode videos are no longer chopped off in responsive design, but adjusted to the width and center aligned.
• The overall appearance is now not so angular/edgy.
• A BBcode embedded Facebook video now has localized languages with language tag. #252 (https://developers.facebook.com/docs/javascript/internationalization).
• BBcode: Removed reference to an active lightbox plugin, as PhotoSwipe can be used as an alternative.
• Fixed an error in the HTML code of PhotoSwipe-Plugin. #253
• PhotoSwipe 4.1.3 (2019) included. #255
• In the admin area, the configuration panel has been revised
• fixed vertical alignment of BBCode toolbar in write panel
• Lucida Console [code] ... [/code]is now correct as a font in the CSS file.
• Removes obsolete acronym element in the language files and replaces it with the appr element
• The theme now adapts better at screen widths between 720px and 768px.
• Fixes a problem in the admin area when rendering font-sizes in Safari, Chrome and Firefox (iPhone/iPad). #256
• Admin area now has Leggero-v2 style background instead of white background.

With best regards Frank