Participated: Fix pagination issues.
Participated: Add count to sidebar item and fix discussion data.
Participated: Fix formatting and remove unnecessary lines.
Participated: Remove problematic uncached Count and fix spacing.
Participated: Change tabs to spaces.
Optimize the pager on the participated plugin.

- Don’t calculate the count of participated discussions.
- Use the prev/next pager instead of the numbered pager.
- Remove trailing whitespace.
Merge pull request #171 from vanilla/hotfix/participated-pagination

Participated pagination