[tkt-10] Adds ImageFinder class

This class should be used for any image file name/folder manipulations.
Right now it provides `getThumbnailFileName` which returns unique
path for a thumbnail image using first three characters from md5 hash
as a folder name and the rest as a file name.

All Commands are now using it to get all kinds of thumbnails files or
folders.
I will revert this change, it was only for debugging and I forgot to roll it back :disappointed: