Now all buttons have a css-class specifying its function

It is now possible to hide edit- and collapse-buttons like this:

    <style>

        .json-editor-btn-edit
        {
            display: none;
        }

        .json-editor-btn-collapse
        {
            display: none;
        }
    </style>
Merge pull request #87 from mbknor/specific-button-classes

Now all buttons have a css-class specifying its function
First pass at laying out the form in a grid.
Improve grid layout algorithm and appearance of multiple/enum/select editors.

Fix bug with link holder messing up table rows.
Temporarily get rid of add/remove property links. (will combine functionality with "add property" button eventually).
Merge branch 'ui-improvements' of https://github.com/jdorn/json-editor into ui-improvements
First pass at EditJSON and Properties modals.

TODO:
*  theme the modals
*  take minProperties and maxProperties into account