Add support for log scale axes

This is a PR for #703 
For reference, it should be:
```
if x_axiscls:
        if x_axiscls is LogAxis:
            p.x_mapper_type
        xaxis = x_axiscls(plot=p, dimension=0, location="min", bounds="auto")
        xgrid = Grid(plot=p, dimension=0, axis=xaxis)

    y_axiscls = _get_axis_class(y_axis_type, p.y_range)
    if y_axiscls:
        if y_axiscls is LogAxis:
            p.y_mapper_type="log"
        yaxis = y_axiscls(plot=p, dimension=1, location="min", bounds="auto")
        ygrid = Grid(plot=p, dimension=1, axis=yaxis)
```