Remove request dependency from botframework-connector library

[stevengum]

Fixes #600

Description

This PR removes the request dependency in the botframework-connector library and instead uses node-fetch and form-data which should allow botframework-connector to be used in the browser.

Specific Changes

• EmulatorApiClient, MicrosoftAppCredentials, OpenIdMetadata classes no longer use request
• Reworked some of the private and internally called methods to use async syntax as opposed to Promises or worse, Promise-callback style

Testing

• All current tests still passing
• Bot works with Bot Channels Registration
• Browser bot (webpack without errors due to botframework-connector)

[justinwilaby]

Some small, tiny opportunities for terseness. Other than that

[coveralls]

Pull Request Test Coverage Report for Build 2149

• 29 of 43 (67.44%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.07%) to 82.159%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
libraries/botframework-connector/src/auth/openIdMetadata.ts	13	16	81.25%
libraries/botframework-connector/src/emulatorApiClient.ts	0	5	0.0%
libraries/botframework-connector/src/auth/microsoftAppCredentials.ts	15	21	71.43%

Totals
Change from base Build 2139:	0.07%
Covered Lines:	2626
Relevant Lines:	3079

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💛 - Coveralls