WIP: CS-5224: Allow custom memory_limit for composer

Allow custom memory_limit for internal composer and plugin related system calls.

Adds a few plugins to newscoop and suddenly composer requires a lot more memory. Maybe a lot more memory then you want your php to access. For manual calls it's easy to add the -d option to the php call and set the memory_limit to 1024M. But Newscoop does some internal calls and this should help you out with that.
as not AS