Allow to style transcluded Images

Macros that transclude images from remote servers require means to align them easily. Therefore we should add attributes to add style and css attributes to a surrounding container.

Maybe we can integrate it into the standard image feature: https://confluence.atlassian.com/display/DOC/Displaying+Images

<ac:image ac:align="right" ac:thumbnail="true" ac:width="128">
  <ri:attachment ri:filename="icon-128x128.png"/>
</ac:image>

<ac:image><ri:url ri:value="https://example.com/logo.png" /></ac:image>