Add declaration of db module methods

[james-owen]

This addition is simply to aid users who are looking for the initialization of the db methods that are used throughout amphora. Users can search for these methods in the /services/db.js file, which makes the connection do a db module easier to trace and to understand.

[coveralls]

Pull Request Test Coverage Report for Build 2150

• 9 of 9 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 2148:	0.0%
Covered Lines:	4483
Relevant Lines:	4483

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💛 - Coveralls