Reduce the size of the title image and center it

Currently, the title image consumes a whole portion of the window. I played around with the settings and following configuration looked good to me:

.title-image {
    ...
    padding-top: 14rem;
    padding-bottom: 12rem;
    background-position: center;
    ...
}

Additionally I added the background-position option and set it to center.

@hueser93 @erxleb87 What do you think?