Cache themes and retrieve from cache when available

[banani720]

Description

This pull request caches the theme data with an expiry date of 30 days to local storage. If a theme exists it is returned and no call to the CDN to get the theme are made

Closes #85

What change does this PR introduce?

Please select the relevant option(s).

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation update (changes to docs/code comments)

What is the proposed approach?

To resolve this issue I simply added cache setting/getting functions in order to check for a cached theme before going to the CDN. If there is no cached theme or it is expired, a call to the CDN is made and the result is then cached for future use. I chose 30 days as an arbitrary number but we can expand or reduce that as needed

Checklist:

• [x] The commit message follows our adopted guidelines
• [x] Testing has been done for the change(s) added (for bug fixes/features)
• [x] Relevant comments/docs have been added/updated (for bug fixes/features)

[banani720]

Hey @tjtanjin I'll get right on that, appreciate the feedback!

I had just one question regarding your third bullet, is the idea that the CSS styles text SHOULDN'T be cached?

[banani720]

In the meantime, I've gone ahead and implemented a unique key for cached themes so that they don't overwrite and reworked getCachedTheme and setCachedTheme so that they handle undefined versions when setting cache keys. I've also gone ahead and redone the cache theme key to be rcb-theme in accordance with the naming standards I've seen elsewhere in the repo.

[tjtanjin]

Hey @banani720! Are you still working on this PR? If you require further clarifications feel free to ask 😊

[tjtanjin]

Any updates @banani720? 🥹

[tjtanjin]

Succeeded by #103