Soft-couple Language package to Filter package

This makes the Language package dependency for the Filter package
optional as it is is only required when `OutputFilter::stringURLSafe`
is used by the application.
Add joomla/language to require-dev
Invalid composer.json
Updating required versions for packages

Updated the required versions of dependencies to "1.*".
Removed "minimum-stability".
Adding the DI package to the sub-splitter.