load only one stylesheet for all modes instead of three

Instead of three stylesheets for 'all', 'screen' and 'print' modes, they are all loaded into a single stylesheet by wrapping all screen styles in a "@media screen {}" and all print styles in a "@media print {}". The 'all' mode is not wrapped in anything.
Potential issues with existing CSS: If any of your screen or print CSS files already contain any "@media" syntax, the CSS will probably break. In that case please add any CSS with "@media" in it to the 'all' mode instead!

Also, the 'rtl' mode is hereby deprecated. Please just prefix any RTL styles within your normal CSS files with "[dir=rtl]". This also fixes that RTL styles cannot be added for 'all' or 'print' modes.
moved the mobile part of the rtl styles (including @media) into mobile.css
minor changes to gradients: quotes around data-uris and commented css solution
moved contents of rtl.css into other CSS files
rewrote and improved HTML for TOC

Attention: Template authors need to adjust their CSS!

Original structure:
div.toc >
  div#toc__header.tocheader.toctoggle > span#toc__toggle.toc_close|toc_open > span
  div#toc__inside > ul.toc > li.level1 > div.li > span.li > a.toc

New structure:
div#dw__toc.open|close >
  h3 > strong > span
  ul.toc > li.toc > div.li > a
improved HTML for search results

Attention: Template authors need to adjust their CSS!

Original structure:
div.search_result >
  a.wikilink1 > span.search_cnt
  br
  div.search_snippet

New structure:
dl.search_results >
  dt > a.wikilink1
  dd
added accidentally removed jquery-ui styles back again
moved plugins' rtl.css to their style.css counterpart (part of FS#2185)
added minimal RTL print styles (part of FS#2185)
when there's not enough space for images, make sure they stay proportional (might be FS#2480)
commit to trigger report generation
Arabic Language Update
Added page title to search results in Remote API
Remote search is aware of useheading option
Marathi language update
Romanian language update
made it possible to disable HTML mails in the config
changed internal Mailer members from private to protected
Merge branch 'master' into htmlmail

* master: (382 commits)
  Romanian language update
  Marathi language update
  Arabic Language Update
  when there's not enough space for images, make sure they stay proportional (might be FS#2480)
  added minimal RTL print styles (part of FS#2185)
  moved plugins' rtl.css to their style.css counterpart (part of FS#2185)
  removed all browser-specific gradients as the recently (in 42ff6730) introduced svg makes them unnecessary
  removed comments from accidentally commented lines in tpl_includeFile()
  removed obsolete template file
  added tpl_includeFile() to core
  Make getTitle method in remote interface public
  Changed an error code in XML-RPC interface. This error hasn't anything to do with the rest of the -32600 errors.
  BG: language update
  Korean language update
  fixed performance issues with gradient in Firefox (which also added gradient support for IE9) (FS#2447)
  deleted very old (and unused) images
  added accidentally removed '<?php' back in (was in 57fc5edd)
  wrapped X-UA-Compatible meta tag with conditional comments
  added explanation to todo in _forms.css
  removed problematic 'overflow: hidden' from lists again ('unfixes' FS#1950)
  ...

Conflicts:
	inc/auth.php
	inc/load.php
rearranged the config options

We had a lot of options lumped together under "Advanced Settings". I
introduced two more categories and move a few options to other existing
categories.
I also reordered the appropriate entries in the source files to make it
easier to find stuff when extending the options.