Change the layout manager

```
The GridBagLayout used in the application is impractical to make changes to the 
UI. For example it's impossible to align the "Source" and "Target" borders 
while preserving the alignment of the fields in the two boxes.

I suggest switching to a versatile layout manager like MigLayout.

```

Original issue reported on code.google.com by `ebo...@apache.org` on 5 Apr 2011 at 10:55
