Fixes and improvements

• Add PKCE support for OpenID Connect (#134) (@onyedikachi-david)
• Fix settings panel on tablet-sized screens (#121)
• Fix question counting for quiz component
• Fix embed deletion bad keys for attendees
• Fix event name length validation (min: 5, max: 50)
• Fix event code length validation (min: 5, max: 10)
• Fix presentation upload progress when editing an event