Support Theme: Replace div:nth-child selectors with classes

[SergeyBiryukov]

The theme uses a couple of cryptic div:nth-child selectors to hide "Browse Plugins" and "Search Plugins" blocks in the sidebar for plugin support topics (same for themes).

This leads to inadvertent hiding of "Feeds" and "Tags" blocks in Pending/Spam views.

Explicitly defined CSS classes should be used instead.

[SergeyBiryukov]

It looks like these sections are never actually displayed anywhere. They are added on plugin and theme support/review topic lists, but end up being hidden in the theme.

meta-2495.2.patch​ removes them to prevent further confusion. Any objections?

[SergeyBiryukov]

meta-2495.2.patch​ was too overzealous, it removed the plugin/theme info section too.

meta-2495.3.patch​ is the way to go.

[SergeyBiryukov]

In 4948:

Support Forums: Remove plugin- and theme-specific sidebar sections that are never displayed in the new theme.

See #2495.

[SergeyBiryukov]

In 4949:

Support Theme: Remove plugin- and theme-specific sidebar section styles that are unused since [4948].

Fixes #2495.

[SergeyBiryukov]

In 5755:

Support Forums: Remove "About this Plugin/Theme" heading that is never displayed in the theme.

See #2495.

[SergeyBiryukov]

In 5756:

Support Theme: Remove styles for hiding the "About this Plugin/Theme" heading removed in [5755].

See #2495.