Provide a cleaner method of specifying default plot tools

[stefanmeili]

I really dislike the default scroll to zoom option in holoviews. I find it hijacks scrolling in my notebooks and messes up my plots instead of being useful.

I've found it is possible to disable this by setting:
hv.plotting.bokeh.element.ElementPlot.active_tools = ['pan']

per this thread:
https://discourse.holoviz.org/t/best-way-to-turn-off-zoom-tool-by-default/5590

However, it's a little verbose and I have to track down the last notebook I used it in every time. I'd really appreciate an easier to use option such as:
hv.extension('bokeh', active_tools = ['pan'])

or:
hv.output(active_tools = ['pan'])

or
hv.opts.defaults(active_tools=['pan'])