Date picker for time range selection

[Treora]

This builds further on @RajPratim21's work of #74, to resolve #26. Main changes:

• Make search independent of the store again (pass date range as arguments).
• Clean up code and css.
• Style UI a bit.
• Refresh search results when date range changes.
• Also apply the date filter when no search query is given.

Comments are welcome, otherwise I will merge it as is in a few days.

[RajPratim21]

@Treora , Thank you for your help, Once you merge it I will make the required changes in the PR #75 for natural language date parser, as they are working in same style, to maintain the integrity.