UI: Proposal view improvements

[ta-lind]

Figma preview/specs: https://www.figma.com/file/1pSibJb3COXW39IJJvzxJ8/decred---piui----politeia?node-id=614%3A2066

This is mainly addressing the recently added proposal info section, as well better clarifying the voting details. The more compressed voting cards in the proposals list view (index) remains for the most part unaffected.

1. The new proposal details covering domain, amount, end and start dates use the same pattern as in CMS design overhaul.

2. Textual "← Go Back" replaced with larger icon button as in Decrediton/CMS update for consistency.

3. Version control is simplified to "ver." and instead of the bullet point there is now an icon before it. The icon should be have a grey (inactive) variant while proposal is at version 1, and switch the element color from #596D81 to #091440, as well display the dropdown arrow next to it. No changes in proposal list.

4. Addressing user feedback regarding better understanding quorum. The yes/no vote and quorum are split into two progress bars for easier sense-making. While the quorum has not yet been reached, the bar displays and X icon and uses a #091440 background for the progress bar, which is filled with #8997A5. Point of this is to display the quorum progress bar as more active while it's not yet reached, and less active (grey) when it's reached. On hover displays tooltip info if the requirement is met or not.

5. The Yes/No vote bar is therefor simplified. There is also more clarity around the 60%, marking it with a bolder stroke and indicating a circle that displays the current winning result color (green/orange).

6. Proposal summary included a refined layout and icons for the footer components.

7. The components in the proposal list remain otherwise unchanged, except the 60% stroke could be the same style (thickness / color) as in the update. Also in the current release a unnecessary grey stroke is surrounding the progress bar.