Add getConfig() to layers Concatenate and Bidirectoinal

[caisq]

with unit and integration tests.

Fixes: tensorflow/tfjs#328

BUG: Fixes the saving and loading of Concatenate layers (tf.layers.concatenate).

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This change is 

[bileschi]

Review status: 0 of 5 files reviewed at latest revision, all discussions resolved.

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integration_tests/tfjs2keras/tfjs_save.ts, line 111 at r1 (raw file):

Functioal

Can you fix this spelling error while you're in there? Thansk ;)

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src/layers/wrappers.ts, line 475 at r1 (raw file):

// TODO(cais): Add logic for `numConstants` once the property is added.

Would it be safer to throw NotImplementedError if the object has a numConstants?

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src/layers/wrappers.ts, line 486 at r1 (raw file):

    // TODO(cais): Add logic for `numConstants` once the property is added.

Probably no need for the TODO, given the NotImplementedError

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Comments from Reviewable

[bileschi]

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Review status: 0 of 5 files reviewed at latest revision, 3 unresolved discussions.

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Comments from Reviewable

[caisq]

Review status: 0 of 5 files reviewed at latest revision, 3 unresolved discussions, some commit checks pending.

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integration_tests/tfjs2keras/tfjs_save.ts, line 111 at r1 (raw file):

Previously, bileschi (Stanley Bileschi) wrote…

Functioal

Can you fix this spelling error while you're in there? Thansk ;)

Done.

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src/layers/wrappers.ts, line 475 at r1 (raw file):

Previously, bileschi (Stanley Bileschi) wrote…

// TODO(cais): Add logic for `numConstants` once the property is added.

Would it be safer to throw NotImplementedError if the object has a numConstants?

this.numConstants is currently undefined.

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src/layers/wrappers.ts, line 486 at r1 (raw file):

Previously, bileschi (Stanley Bileschi) wrote…

    // TODO(cais): Add logic for `numConstants` once the property is added.

Probably no need for the TODO, given the NotImplementedError

Let's keep this TODO item. It's better to be redundant than to miss something.

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Comments from Reviewable