Bugfixes and backend maintenance

• Added snapshot compression in database
• Added snapshot merging based on time and author
• Added absolute timestamps hints where necessary
• Simplified routing in backend - changed Controllers to Routes
• Renamed SearchServices directory to Search
• Renamed Controllers/ViewProxies to ViewProxies
• Improved MySQL integration
• Improved test database upgrade script
• Changed PUT requests to POST
• Changed base64 uploads to FormData JS API
• Removed AJAX external caching, which led to certain anomalies
• Removed download link for YouTube posts
• Fixed backend trying to actually download YouTube URLs - now it redirects to the video instead
• Fixed tests using real DB when they shouldn't
• Fixed bad message when serving non-existing files
• Fixed current search not showing pointer cursor on hover
• Fixed scoremin and scoremax search
• Fixed entity IDs treated as strings, which led to certain anomalies
• Fixed everyone could view every post
• Fixed everyone could feature posts
• Fixed everyone could delete posts
• Fixed link to users and posts disregarding privileges from config.ini
• Fixed precision loss in post disk space usage
• Fixed putting "null" in post sources
• Fixed post note removal didn't generate snapshot