Simplify the quick search info box
Update form styles

- Remove styles from selects, since they are impossible to get
  to look nice across platforms without a lot of hacks (they currently
  looked pretty bad on my Mac)
- Use a focus style that works better with the rest of the design
- Remove monospace from some inputs, and selects. Which inputs should
  have monospace fonts will be decided on a case-by-case basis, matching
  how the text would typically display in a desktop application.
  We might also possibly remove monospace fonts from all single line
  text inputs, as it has limited usefulness.
Make unqualified searches always search in description and summary

This makes the different behaviours differ less from each other. What
happens is basically that you always search summary and description, but
if the term is a single word, it will also look in branches, and if it
looks like a path, it will also look at paths.

This change is also necessary for a coming simplification of the search UI.
Redesign the search page

The design is based on some assumptions:
 - Free text search is common and should search all relevant fields.
 - Owners is the most common user search, so that is the default.
 - If you want to search in a branch, you will often select a
   repository. Their relationship is made clear in this design, with a
   "this-then-that" workflow.

Slightly more Python code at the moment as there are no helpers for
non-table paleyellow sections, but in the long run it's a simpler approach.

The CSS uses flexbox, currently with no vendor prefixes. It is tested in
Opera 12 and Chromium-based browsers, but might be broken in Firefox,
Safari and IE10, but those should be quick fixes.
Add 'text' keyword to search both summary and description
Add owner-or-reviewer as an internal search keyword