Adds the following features to matrix.helmholtz.cloud: * upload of multiple images at once, incl. image captions and tags * browse through all images of one message with left(right keys, and through different messages with up/down * only see chats of the current (sub)space, deeper hirarchy level chats are hidden * see direct messages also while inside spaces * use also on mobile, using Firefox for Mobile browser (aka no app needed) * install as app via browser
