Review code related to spatial pages

There is some duplicated (or very similar) code related to the pages that have equations (surface model param page, stimuli, local connectivity, dynamic), basically those which have equations.

Similar code can be found in the controllers, related HTML pages and some JS functions. Look at the way equations are plotted, look at the events put on the form fields and in some controller methods. They are related to the changes I did for the TVB-O page (https://github.com/the-virtual-brain/tvb-root/pull/529).

Also, with a little work I think that the refresh_subform method can also be generalized for the dynamic controller. It is a little harder because there are 3 subforms and there are other things happening at refreshing, but I think it can be done.