#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.

... 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 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.

(How the hell did they get back in?)

The height handling code was triggered before the width handling code
and thus the right pane was below the other panes during the height
calculations which caused strange effects. Now the height handling code
is called again after adjusting the width of the right pane.

This fixes the section edit highlighting when the start marker (normally
a heading) is inside other HTML elements like a div from the wrap
plugin.

added missing info.txt parameters, added plugin plugin's info.txt, adjusted old default  template's description

This adds more tolerance to the width calculations of the media manager
panes which avoids that the right pane is displayed below the other
panes.