Feat: Add option to only perform input amplification

[lacinoire]

Adds an option to skip assertion generation and only perform input amplification on the test cases.

[coveralls]

Pull Request Test Coverage Report for Build 2515

• 21 of 25 (84.0%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.3%) to 83.567%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
dspot/src/main/java/eu/stamp_project/dspot/DSpot.java	15	17	88.24%
dspot/src/main/java/eu/stamp_project/dspot/common/configuration/UserInput.java	1	3	33.33%

Totals
Change from base Build 2513:	0.3%
Covered Lines:	4948
Relevant Lines:	5921

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💛 - Coveralls

[monperrus]

@lacinoire LGTM , thanks a lot! the failing job is unrelated.

@danglotb merge?

[danglotb]

Thank you @lacinoire

I must fix the failing job in Travis, sorry about that.