Partial fix for plotlyjs backend, for IJulia

[lwabeke]

Tries to address #1793 and JuliaPlots/PlotlyJS.jl#221

IJulia and REPL plotting seems to work again, however from REPL plot! creates a new empty window in addition to updating existing window (this behaviour seems to be similar to master), but only if run on a separate line, running plot(rand(10));plot!(rand(5)) doesn't create the extra window

[mkborregaard]

There are some conflicts - could you rebase your pr on current master?

[mkborregaard]

Thanks. It looks sensible - what's "partial" about the fix?

[lwabeke]

Sorry, weird, if I checkout master, I wasn't getting the modification to _create_backend, but manually removed that part of the change.

I'm still a little bit worried that the conditional write I removed is still required for certain scenarios, but I don't know where and it doesn't work in its old form.

[lwabeke]

"Partial" in terms of cutting away branches, which I can only assume had been required in certain scenarios.
Maybe it should then be only partially tested: From REPL, from localhost using IJulia notebook() and later minimally from Juno.
My guess is the use_remote part that I removed was for JuliaBox or some other setup of using IJulia remotely. Also is there other IDEs where plotting has been integrated, maybe it was for one of them?

Initially I added the partial also due to the fact of a blank plot window still showing up when calling plot!, however it seems that is a seperate bug also in the mainline.

[mkborregaard]

superseded by #1885 . But thanks @lwabeke !