MIPs

This pull request implements: MaxIP, MinIP, MeanIP, MIDA, contour MaxIP and contour MIDA.

* MaxIP (Maximum intensity projection) - compose a 2D image taking the maximum intensities from n slices. Useful to see bone, lung nodes and regions with contrast. Not provides a good sense of depth of the original data.

* MinIP (Minimun intensity projection) - compose a 2D image taking the minimum intensities from n slices. Useful to detect some lung diseases. Not provides a good sense of depth of the original data.

* MeanIP  (Mean intensity projection) - compose a 2D image taking the mean intensities from n slices. Useful to detect some tumors. Not provides a good sense of depth of the original data.

* MIDA (Maximum Intensity Difference Accumulation) - Compose a 2D image taking account the local maximums. It provides good sense of depth of the original data.

* Contour MaxIP - Compose a 2D image using maximum intensity of the contour of n slices. Useful to see the contours.

* Contour MaxIP - Compose a 2D image using MIDA of the contour of n slices. Useful to see the contours. It provides good sense of depth of the original data.