Arduino boards and libraries should be installable without internet

In various situations, ranging from restrictive or expensive venues, to remote areas with poor internet service, it is desirable to be able to install the Arduino IDE (multiple compilers, and libraries) without a viable internet connection.

Ideally, I think you should be able to read the .json files from a directory, and have the content picked from the same place. Perhaps as a preference: "install from: [Internet | " (not unlike searching for new windows drivers, in fact.)

Additional context

Additional requests

• https://github.com/arduino/Arduino/issues/2981#issuecomment-93497749
• https://github.com/arduino/Arduino/issues/2981#issuecomment-312645453