Update for dex 0.6.3

[jholdstock]

• Change download link to read "Download" instead of "GitHub"
• Add news item
• Update download link to 0.6.3
• Revert release note link to 0.6.0. This is a more far more detailed document than the patch release note (which links back to the 0.6.0 note anyway)
• Add link to dex.decred.org

And

• Change color slightly so its easier to see which link you are hovering over.

Closes #1141

[jholdstock]

@xaur I haven't removed the release notes link as you suggested because I don't believe they are meant to point to the same location - I think that was a mistake.

[xaur]

Thanks! I'm good with this as is but just to clarify my reasoning:

I don't believe they are meant to point to the same location

Removing Release notes link works in combo with renaming GitHub (now Downloads) to Download and release notes. That link contains both downloads and release notes, so I believe it can be the same link. Also release notes go first on that page so we achieve routing users through both in the right order.

Separate Release notes link makes sense if we provide direct download buttons like in the Decrediton tile on same page.

Revert release note link to 0.6.0. This is a more far more detailed document than the patch release note (which links back to the 0.6.0 note anyway)

The downsides:

• It may be confusing for users expecting to see what has changed in latest release they are about to download as opposed to last major release
• This way we make a decision which document dcrdex users should read first. It is better decided on dcrdex end and dcrweb could be just a consumer of whatever "release entry point" link they give us. If that link is not good enough at routing users through the important v0.6.0 document it is better fixed on their end by making the existing link bold or something. For example, v0.1.x series were more vocal about it saying "Please read the initial release (v0.1.0) notes for important information and instructions."