Improve new delete button on TOC's layer

[simboss]

There is two things really:

• The color of the X, it should not be red (which indicates an error condition) but it should be of the same color of the other components
• when I click on the X a messa appears asking me if I want to make this change. Let's say I have changed my mind, how can I make this message go away?
• the confirmation message messes up the layout of the buttons as shown below

[offtherailz]

We can use this component instead https://github.com/geosolutions-it/MapStore2/blob/master/web/client/components/maps/modals/ConfirmModal.jsx
or at least a pophover as confirm window. http://react-bootstrap.github.io/components.html#popovers