#159616864 Improve validation logic

[olusoladavid]

What does this PR do?

Improves the validation error responses of the API when a user or client makes a bad request

Description of Task to be completed

• Add more descriptive error messages
• Return all errors found in request instead of single error
• Refactor controllers to have consistent return

How should this be manually tested?

• Run npm test
• All Endpoints will be deployed to https://my-diary-api.herokuapp.com/api/v1

What are the relevant pivotal tracker stories?

#159616864

[coveralls]

Pull Request Test Coverage Report for Build 108

• 30 of 55 (54.55%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.5%) to 80.702%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
server/utils/verifyToken.js	0	2	0.0%
server/controllers/userController.js	14	24	58.33%
server/controllers/entryController.js	16	29	55.17%

Totals
Change from base Build 106:	-0.5%
Covered Lines:	142
Relevant Lines:	168

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💛 - Coveralls