Temporary templates created when plotting

[James-Crean]

When plotting data with vcs-js it looks like temporary templates are being created and are not cleaned up when the websocket is closed. This shows up in vCDAT when plotting some data then refreshing the page. On refresh, vCDAT loads all templates available, which includes the temporary templates created due to plotting.

I believe this may be due to the following line inside of PlotManager.py:

self.dp = self.canvas.plot(*args, ratio="autot")

Specifically, the ratio="autot" part seems to be responsible for creating the template, but there is no code in place to clean it up.

[doutriaux1]

@James-Crean @scottwittenburg I think we need to clear all the canvases before we get the list back. It will remove tem p templates. We do need the aspect ratio.