#26: ui improvements for extension popup

[KoustavFrost]

Issue: #26 and #31 (Both are related and UI issues, hence clubbed together)

Changes:

• The color scheme of the Overall Activity has been improved and also a legend has been added for more clarification.
  
• Some help texts have been added to make the user understand the sections more clearly
  
• A monthly section has been added in the Details page
  
• The color scheme of the delete buttons have been changed to make it more clear to the users
  
• The Whitelist and Blacklist sections have been overhauled. The text input box can take comma separated values.
  
• Validations has been added for Whitelist and Blacklist sections
  
• The list has been given a fixed height and post that the overflow is made scrollable.
  
• Pressing enter also creates Blacklist and whitelist entries.
• There was an error where the final time was shown in negative, that has been resolved.