Added support to specify relative time in seconds in DateTrait.

[tannguyen04]

Checklist before requesting a review

closes #228

• I have formatted the subject to include ticket number
  as [#123] Verb in past tense with dot at the end.
• I have added a link to the issue tracker
• I have provided information in Changed section about WHY something was
  done if this was not a normal implementation
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• I have run new and existing relevant tests locally with my changes, and
  they passed
• I have provided screenshots, where applicable

Changed

Screenshots

[AlexSkrypnyk]

@tannguyen04
I understand what you tried to do with BASETIMESTAMP, but this is not the way.

Please make the following changes:

1. Remove base timestamp and introduce dateNow() method that will be returning the time().
2. Override this method to return a preset value in FeatureContext.php - this will allow to mock the current timestamp.