Support composite builds

[guptadeepanshu]

When detecting a composite build (settings.gradle is in a different location than build.gradle), the script should use -p option to specify the build location.
In addition, it should special case buildSrc directory. This will make running tasks from buildSrc as simple as cding in buildSrc and running the task via gw <task>

[dantesun]

Could you provide more details? Even better if you could provide an example project showing what's the issues.