Reviewed DB Adapter input filter

- Added error messages
- Normalized unit tests
- Use `init()` method instead of constructor
Reviewed Module input filter

- Use `init()` instead of `__construct()`
- Add error messages
- Normalize unit tests and add additional test cases
Reviewed Version input filter

- Added regex validator to version
- Added error messages
- Use `init()` instead of `__construct()`
- Normalize unit tests, and add more test cases
Reviewed all module-specific validators

- CS fixes
- Some minor logic fixes:
  - test PHP keyword case insensitively
  - separate keyword test from regex
  - implement regex for mediatype validation