#2541, alter section highlighting to insert a container into the DOM to hold the elements being highlighted & later remove it

note: we recommend to NOT use H1 elements in the sidebar for semantic
reasons

Replaced it by the old tpl_include_page() and made it more flexible by adding a boolean $propagate parameter.
(It's false by default for backwards compatibility reasons. Should it rather be true? That would probably be what most users want.)

This reverts commit ea62d531.

Update template footer with HTML5 icon (FS#2619)

This fixes the problem that $PARSER_MODES was sometimes unset by PHPUnit
between test functions that called p_get_parsermodes() as PHPUnit tried
to restore the global environment. I couldn't reproduce this when I
executed all tests but just when I executed a single plugin test.

This problem was reported in https://forum.dokuwiki.org/thread/8143.
Apart from warnings you could notice that when you have namespaces "foo"
and "f.o" and you open the sitemap for "foo" that "f.o" is opened, too.

... because it made the solution less transparent, more error prone and even more like a hack than it already was

This reverts commit 20391a36.

This prevents buffering of the cache file output.

This fixes several problems:
- the CSS cache was only updated when either the CSS files for all media
  types or one of the global files was modified
- when only the screen CSS was changed, the screen CSS was regenerated
  but then the cache was printed which either caused duplicated screen
  CSS output when gzip output was disabled or invalid output with gzip
  enabled as first the plain text screen CSS and then the
  gzip-compressed cache file was printed

Now first all CSS files are collected, then the cache is checked once
and only after this the CSS content is collected.

this is a temporary and somewhat ugly fix. digest subscriptions should
make use of the inline format just as the 'every' subscriptions do.
But it makes sense to implement it correctly in the subscription branch
instead and not introduce new code in the RC.

The link doesn't exist in the English version and it doesn't work
anymore because appending a parameter to a link doesn't work when the
link is not just a URL but an HTML link

This fixes error messages about invalid plugin names for directories in
the plugin directory which didn't contain any plugin. Now the message is
only displayed for plugins which couldn't be loaded because of the
invalid name.

This simplifies a while loop in the js_compress() code. The
functionality of the new code is completely identical to the old code
but it uses less comparisons and according to FS#2593 it is thus a lot
faster.

According to the documentation the function was removed in PHP 5.4.0
though it still seems to exist in my PHP 5.4.6 installation.

This fixes the problem that media items in the feed got the title of the
previous item when useheading was enabled as no metadata is loaded for
media entries and thus the previous metadata was used again. This also
fixes dates for media files.