feat(#495): Change outdated twitter icon

[ahmedhalac]

Closes #495

[ezwelty]

@ahmedhalac Thanks! Since we are going through the trouble, I would suggest embracing the X name more since it seems to be here to stay:

• X-Twitter.svg → X.svg
• XLogo → X (to match the other social media icon components, if this is a valid component name)
• Update alt and title text from "Twitter" to "X"

Visually the X logo is less bold than the other social media icons we are using, but this feels like a detail.

[ahmedhalac]

I wanted to rename it, but it looks weird to me as just ‘X.’ However, I will make these changes.

Btw I used the same color as the other icons have.

[wbazant]

@ahmedhalac can we add <path stroke="#9b9b9b" stroke-width="0.7" to the .svg? https://stackoverflow.com/a/37687733 told me that this is how one can make an .svg appear thicker, and it seems to work. 0.7 seems more or less right after trying a few values, but if you have a way to do it, you could set the value so it matches exactly the thickness of the instagram icon.

[ahmedhalac]

Looks like this solved bold issue. Thanks @wbazant

Now it looks perfect:

Seems addressed now - icon is bold and files renamed, thanks Ahmed!