Update the OS X development documentation

* Remove some outdated information from the guide
* Add scripts/osx_dev to bootstrap a working development environment
* Add a Brewfile to track binary dependencies
Add site setting for category of topics created by embedding
Merge pull request #1860 from ecuk/embed-category

Add site setting for category of topics created by embedding
Merge pull request #1859 from nragaz/mac-os-x-setup

Update the OS X development documentation
More work on trust level 3 requirements page
BUGFIX: category dropdown was off by 1 pixel
FIX: Hidden icon was missing
Don't show category badges on /category/:slug on mobile, unless there are sub-categories
Version bump to v0.9.8.3
Update zh_TW translation