Generate random emoji

[fwdekker]

As suggested by @casperboone, Randomness should be able to generate random emoji.

I think this should be implemented as a new symbol set. Since there are many emoji, I should be careful with the string length of the symbol set.

Additionally, if users have changed their symbol sets, they may not see the new symbol set in their settings until they reset their settings. This issue may also need to be worked around.

[fwdekker]

Introducing a new symbol set for emoji is not necessary because it is unlikely that users will use these very often. However, users should be able to add emoji if they want.