[SECURITY] Unsafe unserialize of GET parameter in Add-Wizard

If the TCEforms wizard "add" is used, the original opened document
is closed and a new one is created in which you then add a new
element to be related.
In order to "store" the originating document which has been
edited, the Wizard/AddController and EditDocumentController
exchange state data in an URL-parameter.
This state-array is serialized in the EditDocumentController
and again unserialized in the Wizard/AddController from that
GET parameter. Without any checks, every code can be injected
to be unserialized here - even though we just need an array
with some data.
This patch changes serialize/unserialize to json_encode and
json_decode. Since the GET parameter only is used in
conjunction of these two classes it is save to changes the
format how the URL parameters are serialized.

Change-Id: Ic33bfe350573d7d77682afd3d5f55a29bb4837a9
Fixes: #54073
Releases: 6.2, 6.1, 6.0, 4.7, 4.5
Security-Commit: d5a752746df9317a3d1534803079b7a34882bba2
Security-Bulletin: TYPO3-CORE-SA-2013-004
Reviewed-on: https://review.typo3.org/26185
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader
[SECURITY] Remove possible XSS from ActionController Error output

As parameters passed to an ErrorObject can be user input, the
output of those parameters in the ActionController::errorAction() method
could lead to a cross side scripting possibility.

The offending output has been removed without substitution.

Change-Id: I95ca32a176ac32c86f37f4f265c4bcfbe886646b
Fixes: #54074
Releases: 6.2, 6.1, 6.0, 4.7, 4.5
Security-Commit: 7cb972ea49ff33e96cd0f6b1ecab10ed0fed0ef7
Security-Bulletin: TYPO3-CORE-SA-2013-004
Reviewed-on: https://review.typo3.org/26186
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader