Show outdated dependencies

[aschempp]

composer outdated shows a list of outdated dependencies.

Example for current Managed Edition:

contao-components/dropzone      3.12.0    4.3.0     DropZone integration for Contao Open Source CMS
contao-components/highlight     8.9.1     9.9.0     Highlight.js integration for Contao Open Source CMS
contao-components/jquery        1.12.4    3.1.1     jQuery integration for Contao Open Source CMS
contao-components/simplemodal   1.2.5     2.0.0     SimpleModal integration for Contao Open Source CMS
symfony/monolog-bundle          v2.12.1   v3.1.0    Symfony MonologBundle
true/punycode                   1.1.0     v2.1.1    A Bootstring encoding of Unicode for Internationalized Domain Names in Applications (IDNA)

The list is only partially useful, as the user cannot change dependencies of packages. However, we should compare the list to local requirements and tell the user if a local constraint prevents from updating to an available version.

since v1.4 of composer there's also a --format=json flag to get the results as JSON.