A variety of loose ends (#540)

A variety of loose ends (#540)

* misc cleanups.

clang-tidy found the Qstring passed by value.

Attempting to build the GUI without webengine or webkit with Qt 5.15
found the missing QT module (widgets) in app.pro.  It is required by QDialog.

* fiddle with document recipes.

add qmake target to generate gpsbabel.pdf.

drop --load-trace xsltproc options when building document.

set logging level for fop to WARN
by creating $HOME/.foprc if it doesn't exist.
fop doens't have the ability to override this on the command line.

* use .foprc in build tree.

This solves the issue on travis the $HOME doesn't exist.

It also avoids writing to the users home directory.

* fiddle with configure.

* filter with doc version stuff.