This is the second PR as part of the Fleet UI Refresh #38.
The goal of this PR was to insert all updated Fleet assets and remove all old assets. More style changes, including the exact sizing and placement of the new images, will occur in a future PR.
- Replace uses of deprecated Bourbon helpers with raw CSS
- Add autoprefixer into the build chain to prefix the now removed helpers
This process was achieved by running through each of the deprecation warnings and using the following bash function to replace it in all files:
```
function bourbon-deprecate() {
grep -rl "@include $1" ./frontend --exclude-dir=.git | xargs sed -i '' -E "s/@include $1[(](.*)[)]/$1: \1/g"
}
```
For some helpers, this did not result in valid CSS, so manual modifications were made.
Closes#1189#1274
