Wikiful

All changes here are reflected in the wiki.

• Added wiki categories for organization purposes, which can contain both pages and subcategories. Seven built-in categories are added to keep broad categories of features (e.g. blocks, biomes) together.
• Removed the wiki_ prefix from the wiki page and wiki section folders.
• Shrinked the size of wiki section headers.
• Hid the wiki button if no wiki pages are available.
• Added destroyed_block event trigger, with the same configuration as hit_block.