remove outdated selenium tests which were never executed recently.

These tests were created using Selenium's test recorder so they are basically unmaintainable.
remove dummy "functional" test cases (WebTest-based).

These tests were not executed for quite some time and they don't
test anything (besides issuing a request to a certain controller)
remove MediaCore CE copyright header from htmlsanitizer. The (now removed)
copyright header was obviously added by accident during the big "frontend
JS MIT relicensing" in early 2012.

The file contents are licensed under a "simplified BSD license"
l10n/it: updated some missing translations
l10n: recompile Italian catalog
fix "current_url()" behavior by relying on routes' url generation mechanism
instead of simplistic path manipulation.

Previously "current_url()" generated bad urls whenever MediaCore was mounted
in a subdirectory.
l10n/de: update translation
l10n: recompile German catalog
fix bad redirect url after successful login (if MediaCore is mounted in a subdirectory)
admin/CSS: don't center label text for local file upload so translations have a bit more space (as many languages require more space than English)
l10n/de: update translation
l10: recompile German catalog
fix URL generation for MediaCore with "proxy_prefix" configuration (if MediaCore runs behind a proxy)
fix bad path and other typos in Mac OS install docs
include "url_for" tests in test suite
update doc_strings for "is_admin()"/"can_edit()" so they match the actual implementation (version 0.10+)
issue deprecation warning if caller actually uses the deprecated 'item' parameter for 'can_edit()'
default media type in Media.example() is now None (was: VIDEO)
adopt SimpleStation's unit test for XHTML normalization (replacing line breaks
etc) into the new test suite (after a thorough cleanup/rewrite)
remove outdated "permission" tests which only checked file system permissions on the current host