Make the site look better

[mertvn]

Related issues:

• Don't use constant sizes for HTML elements #16
• Looting: Room change arrows should be bigger #17
• Make password inputs hidden by default, with an option to unhide #24
• Make certain text fit in their containers by getting smaller automatically #30
• Fix text underlines stretching under parentheses #35
• Light/Dark themes #36
• Looting: Inventory display should be toggle-able #42
• Use modals instead of window.prompt() and window.confirm() #45
• Display the correct answer titles nicely #47
• Add filters for the room listing #49