Fixes to long-standing Retro.css theme bugs

[Roslot]

Just some CSS tweaks to my Retro.css theme. Simplified a few things and fixed others:

• Time is shown properly on the left (date is intentionally cut off to save space)
• Sidebar isn't wasting a ton of space anymore
• No more dead space when the chat starts up, so messages do get "seen" and marked as read without scrolling down
• Everything still works well with 24 char names
• Someday, if we add a .moduser class to the user list for mods, it'll show a + before their name