Fast Marching Method for image inpainting

This has been ob my todo list for long.

Replaces: https://github.com/scikit-image/scikit-image/pull/663

Rebase was impossible, also it was necessary to reduce the number of commit messages anyway.

I created a commit message in behalf of @chintak. I hope this is fine with you Chintak?
Look at `if i_nb <= 1 or i_nb >= rows - 1 or j_nb <= 1 or j_nb >= cols - 1:` which handles out of boundary pixels. But you need at least one border pixel in the current implementation for the inpainting, otherwise it won't find the closest KNOWN pixel correctly.