Render image DPI values on edit galley screen

[mauromsl]

Is your feature request related to a problem? Please describe.
It could be useful to render the dpi of a given image in the images section of the edit galley page, as well as alert of too high/low resolution on uploaded images. This is particularly important when using images with a restrictive license limiting the DPI resolution of the rendered image.

Describe the solution you'd like
On the images section of the edit galley view, render the DPI for each image, as well as flag images that might be too low or high res