Fix Missing Autoloaders File Type Inspectors

Fix Missing Autoloaders File Type Inspectors

Add file type inspector classes to startup/autoload

- Add FileTypeInspector
- Add ImageFileTypeInspector
- Add FlvFileTypeInspector
FileTypeInspector defined twice

FileTypeInspector defined twice

Concrete5_Library_FileTypeInspector defined in two different files.

- Add if class_defined check to only load one.
Merge pull request #1355 from mkly/fix_missing_autoloaders_file_type_inspectors

Fix Missing Autoloaders File Type Inspectors