Fix Pikaday

What does this MR do?

• Removes code from global namespace
• Upgrades Pikaday
• Fixes bug selecting previous day in PST timezone by following Docs: https://github.com/dbushell/Pikaday#formatting

Screenshots (if relevant)

PST	EST
Screen_Recording_2017-10-13_at_01.38_PM__1_	Screen_Recording_2017-10-13_at_09.40_PM__1_

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Review
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #38986 (closed) https://gitlab.com/gitlab-org/gitlab-ce/issues/38869