Optimizing CSS loading and resources

[ColinEspinas]

This PR tries to fix #6.

Before:

After:

Changes done:

• Icons are now loaded locally
• The icons.css file is now a lot smaller
• Unused icons where moved to the unused.css file (copy and paste icons you need from there)
• All CSS fonts files (Inter and Phosphor) are now loaded as non-critical CSS following those recommendations

This made our performance score jump to ~75 as opposed to the ~45 we where getting.

The points that are to address to increase our score are now related to the main thread being too busy. This issue could be addressed in the future using web workers to optimize some of our components.

[ColinEspinas]

@daoudclarke This file is here to copy and paste icons we would want to use in the icons.css file. It's here for convenience as otherwise you'll need to go on the icons repo to find each icons code.

[daoudclarke]

Makes sense I guess.