add possibility to ignore the language fragment for news urls

[fritzmg]

Currently the language fragment is added to simple news URLs when it is enabled in the system settings. However, since news aliases are unique across all news archives this is not really necessary - thus the "simple news urls" could be made even simpler for this case.

This feature will be added in a major release version, but backwards compatibility with the old behavior could be obtained by adding a system setting like "Add language to simple news URLs".

[fritzmg]

While it is possible to omit the language parameter from the simple news URL, Contao will always create a redirect to an URL with the language parameter, if the setting is enabled. This is done before any call to the getPageIdFromUrl hook and thus cannot be circumvented this way.

[fritzmg]

Note: when using the [i18nl10n] Extension, this feature can probably not be enabled (see also #4)