Some misc QML reorg

• Mass rename references to StatusDelegate to PostDelegate and related items. On that note, more stuff in PostDelegate is named after their true function.
• Context menus now appear for GIFs and videos
• Use upstream ToolButton instead of our custom AbstractButton for interaction buttons. This results in less custom code and very little visually changed. We still use the custom coloring solution.
• Moved InlineIdentityInfo to Components because it's used everywhere.
• Fix posts not being considered empty due to regression in the previous refactors.
• Moved around stuff inside of attachments, no real fixes I think.