Built-in Command Line Tool support plugin provides autocompletion and documentation for any command line based tools. It needs just an xml commands description to support new tool. We plan to add automatic recognition of composer and other popular tools in future, but you can have it working today.
To get Composer dependency manager support in PhpStorm you need to open Settings | Command Line Tool Support and add custom configuration:
Set up alias you’d like to invoke and <php path> <composer path> in Tool Path, and then apply changes.
Then open xml description in editor by pressing and close settings. Copy and paste content of <framework> element from here. Or copy whole description, but then check alias and tool path of Composer in Settings. Voila!
Develop with pleasure!