swtbot: Introducing ImageHelper

swtbot: Introducing ImageHelper

The ImageHelper is a way to compare screenshots quickly and efficiently.
It has many helpers made to aid in comparisson. Each pixel is queried as
an RGB, the image can give the following info:

* its dimensions and place in the screen
* its pixels
* all the pixel values of a query (for sampling)
* a row of the image
* a column of the image

Change-Id: Id7a4c168cad18448a4d0d5c14ef395e05b6f018b
Signed-off-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/44635
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>
Tested-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-by: Hudson CI