added a field for double-click characters to stop selecting text on

The lineedit in question is doubleclick_ignore_lineedit. Everything is aligned, filled in and documented (check the tooltip on the doubleclick_ignore_lineedit to make sure you agree with what I've written).

![workspace 1_384](https://f.cloud.github.com/assets/110988/726626/1ff6e40a-e117-11e2-9201-56c0e0794be9.png)