Cache resources exhausted error with Imagemagick

[satyamtg]

When trying to convert/resize large images, mogrify throws the following

mogrify-im6.q16: cache resources exhausted `BES4j.jpg' @ error/cache.c/OpenPixelCache/4083.

A sample image to test it is attached here

For this particular image, default memory it requires almost 600MiB memory with mogrify (the default being 256 MiB), I tested it by gradually increasing the memory limit of ImageMagick

A related issue on Imagemagick seems to be this

I think a better solution would be to remove dependency on mogrify for resizing and format conventions. Instead, we can use Pillow.

Although I'm not sure at this point, this may be the culprit for #145