Add more response icons

[jdrueckert]

With the introduction of response images, we can give module authors the opportunity to design their dialogues more user-friendly by hinting at the effect of a response with an icon.

Currently, we only have a single icon in this module: arrow icon.
In addition, it's possible to leverage icons from the engine (e.g. icon atlas or other modules. The latter, however, can lead to undesired dependencies.

IMO, providing a basic set of suitable icons for dialogue responses is an easy yet useful task. Some examples from the top of my mind:

• ❎ "This response ends the conversation"
• ❓ "This response starts a quest"
• ❗ "This response completes a quest"