preparing new axes positioning: getAxesPosition()

including helper functions:
- getNaturalFigureDimension
- getFigureDimensions
- getRelativeAxesPosition
Absolute positioning instead of aligning.
Bugfix: getRelativeAxesPosition() with multiple handles
Use the bounding box around the axes to rescale the plot.
Remove unused methods from the original alignment method.
Introduce the helpfer function convertUnits()
use convertUnits() to deal with different units.
convertUnits: implemented `pt` and some clean-up
Use `m2t.currentHandles.gcf` instead of `gcf`
Remove unused functions for axis/pgf corners
Merge 'Alternate positioning'
Output AlphaData to PNG dimensions

Dimensions need to match the figure dimensions.
When alpha = 1, it doesn't make sense pass along the data
Merge branch 'issue297' #297