Obj detection activation sparsity

[jasonlyik]

Added activation sparsity to the obj detection example. Makes the following changes:

• updates spikingjelly modules with nn.ReLU instead of F.relu
• changes NeuroBenchModel.activation_layers() to check for activation module before recursing down the grandchildren, as the spikingjelly neuron model has a nested submodule (surrogate function)
• moved snn.SpikingNeuron as recognized activation module to SNNTorchModel rather than NeuroBenchModel
• cleaned up some commented-out code

[jasonlyik]

WIP, will generate the actual results before merging.