Plots exports too many names

[tfburns]

I don't often use too many packages at once, but I've just found that Plots.jl exports names such as Point, grid, etc.
See
sbromberger/LightGraphs.jl#1574 for background.

Occupying such a broad namespace for plotting seems a tad overzealous and makes it confusing for new users. I request/suggest thinking about carving out a more specific namespace which minimally conflicts with most non-competing plotting packages.