Remove CDN & Implement in-use css from CDN into internal css

[DhananjayPurohit]

Created this pull request in response to issue #517. Removed CDN from all the files serving UI for SentEmailViewer and implemented css being in use from CDN into internal css.

[germsvel]

@DhananjayPurohit thanks for this contribution!

Since we're replacing normalize, and that could potentially change the styling of the email previewer, could you include before and after screenshots for any major browsers like Chrome, Firefox, Safari, and Edge? It's tough to review the PR without being able to see how things change.

[DhananjayPurohit]

Thanks @germsvel for giving it a review!

Attaching the screenshots taken while running on Chrome along with the inspect window.

Before making changes:-

After making changes:-

As you can see the inspect window having CDN before making any changes and replacing the CDN on making changes. I would love to test on other browsers too if there is any possibility of breaking on any browser.

[seivan]

@germsvel @DhananjayPurohit I am not a CSS expert, but I have a few questions that might help here.

First off, is the idea of using SentEmailViewer to give an impression of how the email will look like on the receivers end or just make it palatable for the developer monitoring it?

Because if it's for the former, it's making the assumption that the receiver of said email will have normalize on their client or the email itself will contain it when sent.

Why optimize with a separate stylesheet or CDN since this is a developer plugin and most likely not a front facing feature in other words: is it possible to just embed the content of normalize.css into the HTML directly?

[seivan]

@DhananjayPurohit This doesn't implement everything from normalize.css