Replace all hard-coded font-weight properties with variables

Created by: davidsparks

There are quite a few places where font-weight is hard-coded, i.e. to 'normal' or 'bold'. This causes a headache when using custom web fonts which define font weights in numbers, and in any case, for easier customization it would be good for weights always to be defined in variables.less.

Simply replacing 'normal' with @font-weight-normal and 'bold' with @font-weight-bold, and defining these in variables.less, would save a lot of find/replacing.

Here are the elements/classes where weights aren't set with a variable:

body (implicit), .btn-link, .dropdown-menu > li > a, .radio label, .checkbox label, .radio-inline, .checkbox-inline, .input-group-addon, .popover-title, h1 small, h2 small, h3 small, h4 small, h5 small, h6 small, .h1 small, .h2 small, .h3 small, .h4 small, .h5 small, .h6 small, .lead { font-weight: normal; }

b, strong, label, dt { font-weight: bold; }