Improved thumbnail generating

- Moved thumbs folder to public_html/
- Users can supply custom thumbs of any size and the system will treat
  them like normal image
- Removed distinction between various thumb sizes in file system
- Introduced custom rewrite rule, which isn't exactly good-looking, but
  its benefits far outweigh its shortcomings
- Loading up to 75 times faster (was: 100-300ms, is: 4-10ms on my
  machine) thanks to removal of PHP proxying
Refactored TestRunner and core
Removed legacy functions
Added support for MySQL in test runner
Enhanced support for MySQL
Added HTTP error support
Removed ?json in favor of X-Ajax
Fixed issues with variable types

- False booleans were serialized as NULLs, which lead to problems with
  queries like 'SELECT ... WHERE NOT x'
- Fixed anonymous uploads
- More robust integer and boolean parsing in jobs
Increased readability
Grouped views into file hierarchy
Fixed youtube uploads
Fixed comment previews
Added help to test runner
Improved support for no Javascript
Fixed tag autocompletion
Simplified view management
Added API controller
Added API documentation prototype
Reduced job hierarchy
Fixed assert