Refactor WhatsNew.cs and update the UI

[originalfoo]

• Renamed ChangelogEntry class to Changelog (Entry made it sound too atomic)
• Renamed ChangeEntry struct to Item to make it more discernable
• Applied same naming conventions to the UI
• Changelog parsing code moved to WhatsNew class
  • Having the changelog parse all changelogs was super-confusing
  • Added some error checking, and various other QoL tweaks
• Parsing of changelog lines will terminate after last seen changelog is parsed
  • This significantly reduces the number of changelogs in the UI
  • User will still see all changelogs since the last version (which could be some time ago if they've not played for a while)
  • Once they've caught up to latest version, then that's the ony changelog they'll see until new version comes out
  • Might lessen impact of StackOverflowException - WhatsNewPanel.cs #1314
• Disable autoLayout while populating the scroll / content panel
  • Might also lessen impact of StackOverflowException - WhatsNewPanel.cs #1314
• Tweaked the scrollbar to look a bit nicer
  • Also discovered that autosize property on the sprites had an empty setter :/
• Removed one of the lookup lists and reduced amount of string chopping during parsing
• Call MarkAsShown() from OpenModal() instead of the panel close button
  • This ensures if panel breaks it won't be recurrent problem for users
• Tested in STABLE, TEST and DEBUG builds - seems to work well

[krzychu124]

Looks cool, I hope it'll help with all issues with regards to what's new panel

[krzychu124]

Good idea with moving MarkAsShown() 👍 👏