[GraphRegex] Any node type + ordered inputs / outputs

I propose to make the following improvments to GraphRegex:

• Add a . symbol to designate any node type, like .->Conv;
• Allow to specify the input/output index that must be matched, like Producer-1>Conv for input and Producer|0->Conv for output. -> should probably default to input 0 / output 0. Any input / output may be matched using Producer|*-*>Conv for instance.

This would allow to make robust query like the following:

Pad?-0>Conv#->ReLU?;.-1>Conv#;.?-2>Conv#

or

Pad?->Conv#->ReLU?;(.-*>Conv#)*

• It works regardless of how the parameters are provided (it can be a Producer, or any other node type);
• It works for optional inputs, like the bias;
• It ensures that we match the data input of Conv, and not another input.