Changelog - v.0.2.4

This is a major technical update that lays the groundwork for huge future features like the Arena and Marketplace!

New stuff and fixes:

• Implemented the waifus ownership system. This is a core feature for the upcoming Arena.
• Completely rewrote the "Sell" feature, preparing it to become a full-fledged Marketplace.
• Added a new concept, suggested by @ScottyDo
• Added a "NEW" label to all unviewed summons so you don't miss any.
• Fixed the "Save Image" function when in full-screen mode (thanks, @girlfun).
• Temporarily removed the "standing by back, covering by a towel" concept due to unstable results. It will be back once improved.
• Minor tuning to existing styles and concepts for better results.
• Improved backend logging system for faster bug hunting.