misc changes to client

- button F5 is now caught by the script and refreshes only the query
instead of the whole page
- links to the struct wiki are now available when sql mode is toggled
- sql export is now much more simple: clipboard button is hidden but can
be switched on, and clipboard immidiately shows up on export
- fixed some problems with that case when there is no difference between
any fields and now it has an own error message
- fixed table width and some misc. visual problems
- misc.
- thanks to Kriess for the ideas