Run transforms during build, support transform paths with "[]", and add build command.

[jonsnyder]

Description

This PR includes the following changes:

• Change the saved container.js to be the un-transformed settings. These are the settings that are returned when getSettings is called in the UIs.
• Change the default saved container.js to include environment.
• When the built file is requested, the transforms are applied and external files are written. Before the built files were created when the container was saved.
• Add support for property paths in transforms that include "[]".
• Add a build command. I previously had this change in Build command #92, but after working on this PR I realized that the build command should output the external files too and not just the main javascript file. The CLI build command writes the files to ".sandbox/", the library build command returns a map of filenames to file contents.

TODO: Update this so the edge sandbox works with these changes.

Related Issue

#86 - Transform issue.

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[dgrossen]

Please add a note that this command does not work for mobile extensions and ensure it doesn't output anything for mobile

[dgrossen]

Similar to init

https://github.com/adobe/reactor-sandbox/pull/93/files#diff-b335630551682c19a781afebcf4d07bf978fb1f8ac04c6bf87428ed5106870f5R44