Register plugin class using classname

Rather than using the plugin name use the classname. This allows
multiple plugin classes to registered from a single plugin.
Resolve vcs module naming conflict

The vcs module is not contained in any package. This means that it
can't be import from inside a plugin module called vcs. To resolve
this import vcs in the uvis package to give it a package. It can
then be imported using 'from uvis import vcs'
Fix PlotFactory createPlot(...) function

Rather than creating the factory object, call the registerd "create"
function. Raise a RuntimeError if type has not been registered.
Clean up uvis.sh startup script
Add missing error callbacks

Add error callbacks to log errors to console.