[wasm] Add wasm and new models to the benchmark page

[dsmilkov]

• Add bodypix, posenet, mesh, and face detector to the benchmark page.
• Make sure all the models are as fused as possible (using latest converter)
• Fix mem leak during inference
• Fix a small bug in model config
• Add a dropdown with the backend type

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This change is 

[nsthorat]

Reviewed 3 of 6 files at r5.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @annxingyuan, @dsmilkov, and @nsthorat)

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tfjs-core/benchmarks/index.html, line 350 at r5 (raw file):

      var gui = new dat.gui.GUI();

      await tf.ready();

why do you need both of these?

[dsmilkov]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @annxingyuan and @nsthorat)

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tfjs-core/benchmarks/index.html, line 350 at r5 (raw file):

Previously, nsthorat (Nikhil Thorat) wrote…

why do you need both of these?

don't need it now. removed.