tigefa4u projects Trac

- the tabs in the mainnav are now flowed. Thanks to osimons and coderesort.org for initial inspiration. Also closes #4926, the "funny accents" are gone.
- make the #content <div> stand out and use a bit more spacing around it and a discrete shadow
- highlight for targets is now rounded and better stands out.
- fix position of the ''View changes...'' button in TracBrowser
- use rounded tabs in /prefs
- in custom queries filter panel, use round minus buttons
- tweak rounded panels and make foldable sections look a bit like buttons