fixes positioning of menu elements
fixes z-index for mobile menu at small screen resolutions
fix positioning of .main-wrap because #sub-menu-wrap no longer has layout
bump z-indexes up by factor of 10 to overlay slider
fix for misaligned subscribe icon
add border to borderless text entry area, fixes #201
realign topic legend; fixes #202
Merge pull request #200 from JonathanReeve/master

Miscellaneous fixes:

- Misaligned bbPress forum subscribe icon - Fixes #199
- Add border to bbPress forum editor - Fixes #201
- <legend> CSS alignment - Fixes #202

Props @JonathanReeve.
Merge pull request #198 from christianwach/menu-style
Reposition subscribe icon on bbPress topic pages.

This reverts part of commit a76b989f65, which fixed the positioning of
the subscribe icon on bbPress forum pages, but unintentionally broke
positioning on bbPress topic pages.