Add support for toggling color mode ('night/day mode')

[thavocado]

Add support for toggling color mode ('night/day mode')

This pull request adds support for toggling Chakra's color modes, including the dark mode.

It is easy to use, using the pc.toggle_color_mode() helper:

pc.button(
   pc.icon(tag="MoonIcon"),
   on_click=pc.toggle_color_mode(),
)

No custom styling is necessary to use the dark mode, it is built-into Chakra.

Your night/dat mode preference is stored locally as per the Chakra docs.

I believe this pull request would enhance Pynecone's appeal. Having a dark mode on your site is quickly becoming standard and is desired by many users.

All Submissions:

• Have you followed the guidelines stated in CONTRIBUTING.md file?
• Have you checked to ensure there aren't any other open Pull Requests for the desired changed?

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

New Feature Submission:

• Does your submission pass the tests?
• Have you linted your code locally prior to submission?

Changes To Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you successfully ran tests with your changes locally?

[Alek99]

Nice going to test this locally and then review

[Alek99]

Very nice just tested and works well!

[jakobschlosser97]

is it possible to change the default colors of the dark/light mode?