adding formatting features to tracer dialog in vogleditor

* red dots on the two required fields (http://imgur.com/a/tBmXi)
* validation function to moved to dialog, only enables ok button if both fields have some text (same as before)
* vogl checkbox is enabled/checked by default on non-windows platforms
* the trace file defaults to the system's temp directory under file named "trace.bin" (ex. "/tmp/trace.bin")
* application to trace is stored using QSettings under the "trace_file" key, which is stored when "ok" when the path is fetched from the dialog and loaded when the dialog is initialized--on my system this saved them under ~/.config/Valve Software/vogleditor.conf

[General]
trace_file=/tmp/trace.bin

The vogleditor.cpp code looks more complicated than it is, but I basically removed the if block and collapsed the code as the dialog should always come back from the "accept" state with properly formatted fields.  Also I had to break the button box on the dialog into two separate buttons so I could disable the OK button separately.