fix(extension): allow import class from extension with dash in folder

[sylvainlehmann]

Yeswiki is unable to autoload load class from extension with dash or other namespaces invalid characters in his folder. The createPerformable function does not convert some caracters which are valid in folder name but not in namespace.

The fix use a regexp to extract alphanumeric characters from folder name and create a pascal case string without separators

[mrflos]

well done! Thanks for adding the tests!