settings: add 'TRIG:COUN INF' for 0 or -1

We only have a spin box. So we have to find a value to represent
the infinite (INF) trigger count. 0 or -1 sounds reasonable.
settings: replace rate with resolution

The rate setting is from the FLUKE 45 emulation but we don't
support that. We should stick to the SCPI commands and these only
support a resolution parameter to gain more speed. As this
parameter isn't described completely, we start with DEF, MIN, MAX.
mainwindow: move the display combo box to the top

Looks better if the spin boxes are below.