Minor design change grab-bag 🎉
I started with one simple change and found a few more, so here they are.
### Simplify icon style selectors
All FontAwesome icons have an `fa` class, so just use that.
### Don't override color of code blocks in notes
This was a pet peeve of mine.
| Before | After |
|:------:|:-----:|
|  |  |
### Items with tooltips don't need a 'data-original-title' attribute
This attribute gets added dynamically by Bootstrap's tooltip JS based on the `title` attribute
### Fix Profile > Design live-updating
`ui_blue` wasn't added to the list of classes to remove, so if a user changed to that theme, any subsequent changes wouldn't be live-updated.
This change refactors Gitlab::Theme a bit to make it harder for this to happen in the future with new themes.
### Remove the `has_bottom_tooltip` class
Bootstrap's tooltip JS can read the placement from a `data-placement` attribute.
Further, when we supply the `selector` option to `tooltip`, tooltips will be added to any dynamically-added elements matching the selector, without us having to re-call the `tooltip` method.
See merge request !569
