Makeup Leggero-v2 Style

[Fraenkiman]

This is a PR which merges all the individual commits from #254 and #258.

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. What's more, mobile data traffic now accounts for more than 54% of total traffic, overtaking the desktop computer as the most-used device for accessing the Internet. But PC screens also offer significantly higher resolutions by default today than in 2015, for example. 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.
• The theme now adapts better at screen widths between 720px and 768px.
• Media queries were created for individual device classes (smartphone, netbook, laptop and PC) in order to achieve a better display, especially for mobile devices.
• The overall appearance is now not so angular/edgy.
• 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.
• BBcode-Facebook-Video now uses the latest video player API and the lazy loading mechanism of the browser
• A left or right aligned BBcode video will now be centered if the screen < 960 px.
• 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
• The BBcode toolbar adapted for a better display at the screen width of 640px.
• The menu and submenu in the administration area now also has a "slightly" more modern design.
• Template and CSS from Uploader > Gallery: image texts; button and table adapted to Leggero V2 style.
• 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
• Fixes a problem in the admin area when rendering font-sizes in Safari, Chrome and Firefox (iPhone/iPad). #256
• Added "background-attachment: fix" -workaround for mobile devices.
• Admin area now has Leggero-v2 style background instead of white background.

With best regards Frank

[azett]

Frank, this is just AWESOME work! 😮 Thank you very much!