Converse.js: Unify vertical spacing between chats

[Nyco]

Screenshot:

Problems:

• Spacings are inconsistent between groupchats and one-to-one chats

Proposed:

• Use the same spacing as one-to-one chats spacing for the groupchats
  
  
  
  • It is more relaxing
  
  
  • It is mobile/multitouch-compatible (smartphones and tablets, devices with fingers, no mouse or trackpad)
  
  
  • Lower spacings are difficult to tap/click on mobile on RocketChat
  
  

Examples:

[Nyco]

Thinking out loud: globally, maybe every single item in this sidebar should have spacing with the above and below, whatever it is.

[jcbrand]

This is now done, let me know if you still see some inconsistencies.