Use pixel ratio in StackHelper borders and LocalizerHelper

Got **StackHelper** and **LocalizerHelper** strange behavior when loading AMI with different browser zoom.

In my code I have this (taken from examples):
```
...stackHelper.slice.canvasWidth = ...clientWidth;
...stackHelper.slice.canvasHeight = ...clientHeight;
```

When page is loaded with browser zoom 125% the dashed border is reduced (if zoom is higher than 100%) and Localizer lines is absent at all:
The larger the initial zoom the smaller the area of the dashed border

When page is loaded with browser zoom 100% everything is normal:

AMI: v0.0.23dev (+ Ext JS framework)

Example [viewers_quadview](https://fnndsc.github.io/ami/#viewers_quadview) works perfectly with any zoom so the problem is likely in my code.

Any suggestions where to search?