Update contao35 to 3.5.23.

Version 3.5.23 (2017-01-17)
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### Fixed
Handle non-numeric values when calculating the image margin (see #8617).

### Fixed
Correctly generate the download elements in the back end (see #8620).

Version 3.5.22 (2017-01-16)
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### Fixed
Prevent an endless redirect loop if the page alias is "/" (see #8560).

### Fixed
Correctly parse German dates with two digit years in MooTools (see #8593).

### Fixed
Correctly add new resources to the user/group permissions (see #8583).

### Fixed
Trigger the auto-submit function in the date picker (see #8603).

### Fixed
Call the load callback when loading page/file picker nodes (see #7702).

(taca)