Add .form-condensed

Created by: dyve

The default forms are widely spaced vertically. I propose an add-on class .form-condensed, comparable to .table-condensed to use less space between the lines. If I find the time to make a pull request I will, but for now, here's my local solution:

.form-condensed .control-group {
    margin-top: 0;
    margin-bottom: 5px;
}