Add dependency graph

[simpsora]

Since stacks can declare dependencies on others (via the stack_output resolver), it would be nice to be able to visualize these dependencies.

Much like bundle viz, create a command which outputs a Graphviz (or other format) visualization of stack dependencies.

[simpsora]

@stevehodgkiss can you point me to somewhere in the code which has knowledge of the dependencies (if there is such a place)?

[patrobinson]

@simpsora Checkout this class I created to determine stack dependencies https://github.com/envato/stack_master/blob/a8a44696b2febb38250757f928f3684a096f956b/lib/stack_master/stack_dependency.rb