Provide Drush command to regenerate underlying files for all approved libraries

Problem/Motivation

Sometimes when deploying project updates between multiple environments without files (because files folder can be very heavy) there are missing files for the library_field_entity entities.

Proposed resolution

Provide drush command to generate all needed files.

Remaining tasks

- Review initial version of the patch
- document this feature on project's page and README file

User interface changes

N/A

API changes

N/A

Data model changes

N/A