[TASK] Move typo3/stylesheets to EXT: backend

In order to decouple extensions from each other and to
fasten bonding between files to specific extensions the
folder typo3/stylesheets should be moved to EXT: backend.

Change-Id: I2ecf68e9c8d412c1c9b097db63743bde518f52b0
Resolves: #49747
Releases: 6.2
Reviewed-on: https://review.typo3.org/22048
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind
Reviewed-by: Jigal van Hemert
Tested-by: Jigal van Hemert
[BUGFIX] Files with unclean path indexed multiple times

When adding a file or requesting a file by an identifier
cleanup any . and .. in the path before handing off
to the driver so files are not indexed multiple times.

Change-Id: I324c4637621165a56470fb95864eeff1254f62dc
Fixes: #46989
Releases: 6.2, 6.1, 6.0
Reviewed-on: https://review.typo3.org/19684
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
[FEATURE] Improve BE container view helper

Improve the features provided by the BE container view helper
so that extensions don't need to provide their own so often.
Added features:

- load several JS and CSS files instead of just one
- load jQuery
- load some inline language labels

Note: the old way of loading a single JS and CSS file is preserved
for backwards compatibility, but marked as deprecated.

With this patch all BE modules in the Core can use the default
BE container view helper. The Extension Manager needs some special
initialization which is moved to a dedicated view helper.

The customized BE container view helpers are removed.

Resolves: #49749
Releases: 6.2
Change-Id: I236134451a31f08afe5886337cfb1144dac7ad90
Reviewed-on: https://review.typo3.org/22063
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Felix Kopp
Tested-by: Felix Kopp
Revert "[BUGFIX] Files with unclean path indexed multiple times"

This reverts commit 2219d2280c69b4d39443fb26873b2f1c6096bd0e

This breaks Travis big time!

Change-Id: I7135b9478e01a5f95ad20df3a6b24bb5d9715ec8
Reviewed-on: https://review.typo3.org/22078
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
[BUGFIX] File upload in RTE-Link-Editor throws 500 error

When you want to add a link in the RTE-Editor, you can upload files in
the "File" tab. When you select a file and want to upload it, the
reloaded content in the create-link-overlay will throw an error.

The method is feed with a translation of "none - new file".

Bypass the file or folder lookup if we do not have an integer id
and print the message instead.

Resolves: #48219
Releases: 6.2, 6.1, 6.0
Change-Id: I9e1e6bc84b21fb04608841515ac414eec8c04130
Reviewed-on: https://review.typo3.org/20850
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
[TASK] Namespacing: Use-statement for common classes like GeneralUtility

Change-Id: I43d6ef559b0b46e6302ea891b4d39501a99423a6
Resolves: #49745
Releases: 6.2
Reviewed-on: https://review.typo3.org/22041
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn