Creating preview mode

[vandyliu]

Description:

Creating preview mode, which you can change in your settings to enable micro:bit commands. Test it out!!

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

Limitations:

Please describe limitations of this PR

Testing:

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A
• Test B

Checklist:

• My code follows the style guidelines of this project
• My code has been formatted with npm run format and passes the checks in npm run check
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

[xnkevinnguyen]

LGTM

[isadorasophia]

Cool!