[BUGFIX] Disable the TCA Tree if $PA['fieldConf']['config']['readOnly'] is true.

Disable the TCA Tree if $PA['fieldConf']['config']['readOnly'] is true.
This happens for example in translations of records if
$TCA['my_table']['columns']['my_column']['l10n_display'] = 'defaultAsReadonly'.

Change-Id: I18195bbc3fc6369d56669a5fd5c81103140e7a6c
Resolves: #25888
Releases: 4.6, 4.5
Reviewed-on: http://review.typo3.org/1548
Reviewed-by: Marco Huber
Tested-by: Marco Huber
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader