Video block - UI/UX Enhancements

[pinarol]

This issue is opened to track @iamthomasbishop 's comments on this PR:

#854 (comment)
#854 (comment)

@marecar3 has already started to work on these and we believe it'd be easier to track on a separate issue/PR.

Please note that Video block won't be available publicly even if we merge #854, there's a code piece on the PR that prevents that(similar to code block). We'll be doing these enhancements along with other bug fixes before making video block publicly available.

• Media blocks are difficult to select
• Error state design differences
• Uploading state design differences

I added new items here to address the rest #687 (comment)

[marecar3]

Thanks @pinarol! :)