Added SVG fallback to apps settings popup

This fix issue of calendar app with IE8, see issue report for details:
https://github.com/owncloud/calendar/issues/291
Useless else removed

As suggested by @PVince81 : https://github.com/owncloud/core/pull/6721#issuecomment-32289922
error handling in case a requested app doesn't exists
properly handle app activation for unit testing
updated description of the files encryption app
webdav: return SPACE_UNKNOWN if server do not support quota

Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
don't enable files_external tests
Fix array access syntax for older PHP

There was a syntax error when running tests in PHP 5.3.10.
Merge pull request #6807 from owncloud/enc_updated_description

updated description of the files encryption app
Merge pull request #6810 from kofemann/for-upstream

webdav: return SPACE_UNKNOWN if server do not support quota
Merge pull request #6812 from owncloud/tests-fixcachesyntaxforoldphp

Fix array access syntax for older PHP
add link to documentation
show link to app documentation
distinguish app links from doc links
added website field
Merge pull request #6818 from owncloud/add_documentation_to_appinfo

Allow app developers to add documentation links to the appinfo
Merge pull request #6784 from owncloud/fix-activation-of-unknown-apps

Fix activation of unknown apps
Merge pull request #6721 from tsumi/patch-1

Added SVG fallback to apps settings popup
New user agent for the Freebox added for a specific Content-Disposition header.

The Freebox is the multimedia device of a french Internet provider: Free.
This device provides a seedbox which uses the user agent "Mozilla/5.0".
In the "Content-Disposition" header, if the "filename" key is used with the "filename*=UTF-8''" value, the seedbox does not take care about the header and saves the file name with the origin URL. This fix brings the support for the Freebox users.