implemented safe versions of the classes DateTime and DateTimeImmutable

[Kharhamel]

This allow to redeclare methods such as createFromFormat to throw exception instead of returning null.

[coveralls]

Pull Request Test Coverage Report for Build 243

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 36.159%

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Totals
Change from base Build 223:	0.0%
Covered Lines:	418
Relevant Lines:	1156

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💛 - Coveralls

[moufmouf]

Some proposed changes

[moufmouf]

Thanks @Kharhamel !

Now, we should probably modify Safe phpstan rules to trigger warnings on any use of "new DateTime" or any DateTime factory!