New User Test: "PixTestThreshMap"

Unleashing the full power of the pxarCore getThresholdMap interface:

* Configurable scanning step size
* DAC and DAC range adjustable
* Configurable threshold level (default: 50%)
* FLAG_RISING_EDGE checkbox to scan in both directions

To have this test showing up in your GUI, just add the following to your `testParameters.dat`:

```
-- ThreshMap
ntrig               10
dac                 vcal
daclo               0
dachi               255
stepsize            2
thresholdpercent    50
risingedge          checkbox
cals                checkbox
```