[FEATURE] Allow nested values for crawler

The values passed to the crawler for adding to the POST request
can only be simple values. This patch makes it possible to pass
arrays to \TYPO3\CMS\Messenger\Utility\Crawler::addPostVar()
this making it possible to have more complex marker structures
in the messages (e.g Fluid markers such as {user.foo.bar}.
Merge pull request #1 from fsuter/master

[FEATURE] Allow nested values for crawler

The values passed to the crawler for adding to the POST request
can only be simple values. This patch makes it possible to pass
arrays to \TYPO3\CMS\Messenger\Utility\Crawler::addPostVar()
this making it possible to have more complex marker structures
in the messages (e.g Fluid markers such as {user.foo.bar}.