Fix issues with less

- Fix activity log crash report when mouse-hover in less variables (look in commit 5dc2d08 for activity log)
- Less compiler now correcty display compilation error

To reproduce the less compilation error not being displayed in current version just paste this in a less file:

```CSS 

@imagePath2:'../Images';

div {
    background-image: url('@{imagePath}');
}

div.test1 {
    background-image: url('@{imagePath2}');
}
```