Ignore Duplicate email addresses

[saurabhrajguru]

Fixes #691

Checklist

• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them.
• I updated my branch with the master branch.
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation about the functionality in the appropriate .md file
• I have added in line documentation to the code I modified

Short description of what this PR does:

• This fix Ignores adding duplicate email addresses in To,CC and BCC.
• This fix will only take unique email addresses.
• This fix is implemented on EmailHelpers as well as SendGridMessage Methods.
• Apart from that this also adds "LambdaComparer" in Helper-Utilities.

[SendGridDX]

All committers have signed the CLA.

[saurabhrajguru]

I missed one more thing.
So this one is WIP right now.

[saurabhrajguru]

@thinkingserious I believe this is working fine.
I have added tests to verify that.
Please review and let me know if there is any feedback.

Thanks

[thinkingserious]

Hello @saurabhrajguru,

Thanks again for the PR!

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Team SendGrid DX

[thinkingserious]

Hello @saurabhrajguru,

Thanks again for the PR!

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[childish-sambino]

Closing in favor of #991