Rename kowey_gwt_jsplumb.js to conceptdiagram.js

This was initially meant as a bit of experimental code,
but whether or not we continue using jsplumb, we'll probably
want to have some place for JavaScript support functions
anyway
Centralise initialisation of Javascript support
Remove ununsed repaint_everything support function
Tighten up jsplumb initialisation

Limiting the container a bit seems to make scrolling do the right thing