Tweak arrow size for vector plots to make the tip more pronounced.

Ref #700
Scale arrow glyphs by vector magnitude.

Ref #700
Use a 2D arrow source for vector plots.
Resize vector array to match number of points.

Refs #700, #712.

Not ideal, but at least we can continue on to other rendering bugs.
Fix continent clipping artifacts.

#700
Use thinner arrows.

Ref #700
Update vector test baselines.

Ref #700.
Updating baselines
Merge pull request #705 from UV-CDAT/700-vector-improvements

700 vector improvements