Let User Select Image shape

[kprussing]

Based on Issue 11 on ViTables. Add a dialog so the user can specify the layout of the image in the file, Possible options include:

• Arrays, CArrays, and EArrays
• (W,H)
• (W,H,3)
• (N,W,H)
• (N,W,H,3)
• (N,W*H) assuming W==H
• VLArrays
• (N,WH) assuming W == H
• (N,WH) with another (N,2) array containing (W,H)
• VLArrays containing pickled Python arrays

[kprussing]

Commit 9c443ca addresses 2D Arrays, (W,H), and 3D Arrays, (N,W,H), where one dimension is the “spectral” component.

[kprussing]

Commit 4e5fb86 now handles all cases except the (N,W*H) cases. It also adds a menu option to select the axes which are the width, height, depth, and RGBA.