Updated BS3 form classes

Once more I'm looking to update our approach to forms in BS3. Overall the goals here are:

• simplicity (in code and presentation)
• flexibility (not tying ourselves too close to specific HTML)
• consistency (using the same patterns as elsewhere in the project)

To that end, I've made the following changes:

• Use .form-control for styling form controls instead of list of input types. Fewer lines of code, less specific (meaning easier overrides as input[type="text"] is more specific than .input), less intrusive, and more performant.
• Adds new .form-group class to space out groups of form controls when in vertical mode. (Horizontal forms will continue to use the predefined grid classes.)
• Updates form validation classes to separate HTML and CSS. While not directly applicable to individual inputs, the markup is very flexible given the classes we use.

Still needs refinement I think, but overall I like it.