#WAF Added the changes of web application firewall for application gateway

[jobatzil]

Description

• Added new web application firewall features for application gateway
• Updated to the 2017-03-01 Api version of Network component.

Azure/azure-rest-api-specs#1052

IMPORTANT
First commit contains the ApplicationGatewayWebApplicationFirewallConfiguration changes while
"#WAF set x-ms-flatten to true for ApplicationGatewayFirewallRuleSet." contains the changes for the new api call!

"Conflicting" PR: #2943
(This PR doesn't contain the swagger changes added by the PR related to the above link)

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[msftclas]

@jobatzil,
Thanks for your contribution as a Microsoft full-time employee or intern. You do not need to sign a CLA.
Thanks,
Microsoft Pull Request Bot