Wiki: Update standard plugin documentation

[azett]

https://wiki.flatpress.org/res:plugins is reworked and now displayed as a nice table.
This should also be done with https://wiki.flatpress.org/doc:plugins:standard - also, each of the standard plugins listed there needs its own wiki page (just like the community-contributed plugins).

[azett]

The standard plugins pages is reworked, now we may add a page for each plugin with a little more information (maybe screenhsots).