feat(config): Mongoose 4.11 upgrade (#1818)

[GulajavaMinistudio]

Upgrades Mongoose to 4.11.1

Updates Mongoose connection implementation to accommodate deprecated
features & connection options.

Also, updates the Gulp Mocha tasks to reflect changes to the Mongoose
implementation.

Fixes tests to get the database from the existing Mongoose singleton.

Derives from changes in meanjs#1816

Closes meanjs#1814

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Yahoo authentication idea proposed by @codydaig
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