Accent colour in Raw theme is too low contrast

The new Bootstrap-based Raw theme is mostly pretty good in terms of accessibility, but the bright green accent colour used on buttons and links isn't high enough contrast to meet WCAG 2 guidelines. According to http://leaverou.github.io/contrast-ratio/ the contrast ratio between the #629600 highlight and the white background (or foreground) is 3.6 where it needs to be at least 4.5. Since the Raw theme will probably be the basis for a lot of custom themes, it's quite important that this is made more contrasting.

Affects latest master