Don't overwrite bootstrap error, success and information alert colors

http://getbootstrap.com/2.3.2/components.html#alerts

git blame doesn't reveal any useful information as to why this was added in
the first place.
Use bootstrap button color instead of the same color for all button types
Leave non-wysiwyg text areas alone

as was the intention according to the comment above the CSS rule.

Without this regulating the size of the textarea with
attrs={'rows': x, 'cols': y} was not effective.
Bigger font for inputs
Remove unused CSS

There's no category-selected in the Dashboard as far as I can find
Actually use the variables from variables.less
Set a bigger font size and more readable font

The previously used font was too thin.
Visually connect tabs with tab content through a well
Don't mess with my CSS like this!
Use more down-to-earth z-index.

The effect is the same.
Remove deviations from stock bootstrap that caused problems

They came into oscar mostly in several-1000-lines commits with messages
like "dashboard improvements", so there's no way to find out why they were
added.
Reduce whitespace above black bar at the bottom and the form above
Undo border color changes that didn't catch all borders
Add CSS to vertically align plain text with the label in a horizontal form
Undo this bootstrap modification. It makes things harder to read.