ENYO-690: Initial conversion function / mixin.

### Issue
We need a general method for converting length units to resolution independent units.

### Fix
Due to issues implementing user-defined functions in LESS, we utilize a flexible mixin.

### Usage
Original LESS:
```
.myClass {
    height: 100px; 
    margin: 10px 5px 20px 0px;
    border: 1px solid black;
    color: white;
}
```

Updated LESS:
```
.myClass {
    .rI(height, 100px);
    .rI(margin, 10px 5px 20px 0px);
    .rI(border, 1px solid black);
    color: white;
}
```

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>