add ability to read raid info from raid boss image

[vhuynh3000]

This adds the ability to extract the text (gym, pokemon name, and time remaining) from the raid boss screen. The text extract functionality works for most images but it does have some problems when the raid boss covers the pokemon name.

It uses opencv for image processing. The node-opencv npm module is a wrapper around the native opencv libraries so opencv needs to be installed (I used dnf install opencv opencv-devel on fedora 26).

It also uses tessaract for text recognition. The npm module is javascript version so no additional libraries are needed.