All events_test, external_test and search_test classes:
- Namespaced with component[\level2-API]
- Moved to level2-API subdirectory when required.
- Fixed incorrect use statements with leading backslash.
- Changed code to point to global scope when needed.
- Fix some relative paths and comments here and there.
- All them passing individually.
- Complete runs passing too.
Special mention to lib/external/tests/external_test.php:
- external is not a valid component
- hence, its only valid namespace is "core"
- also, it's testing lib/external/externallib.php
- hence, the file (and class) have been renamed to external_externallib_test.php
(to avoid conflicts with other external_test that may exist in core)
