Update from Bootstrap 2 to Bootstrap 3

[Dunedan]

This commit updates Bootstrap from 2.1.1 to 3.3.4. As it's a jump to a new major version with backward incompatible changes, a lot of adjustments have been necessary.

Beside the necessary adjustments resulting from the update, I did the following additional ones to improve the experience with binder:

• As Bootstrap 3 is mobile first, a responsive design hassn't been that hard, so I implemented that. I'm pretty sure it's not perfect yet, but a major step into the right direction. As part of making binder responsive I moved the menu to the top to take up less space on mobile devices.
• Improved vizualization of errors in forms, with highlighted form fields, which contain the invalid data.

[Dunedan]

As you did the update to Bootstrap 3 on your own in the meantime (41f78b3effcf89975c522b4791151233ece9e17e) I guess I'll have to go through the changes introduced by this pull request again to extract to useful design changes. I'll open up one or multiple pull request once I've done that.