Hability to detect error during install/uninstall of shipping extensions with optional install/uninstall methods

Improved call to install/uninstall method (if it exists) on shipping extension, now it can handle errors encountered during install/uninstall process, before this improvement the response was always success no matter what the result of the process.

The response of the method (if it exist) in the shipping extension, must be compatible with the response of an absent method, thus: return false on success and return true on error.