allow editing the same message multiple times

[lara-rium]

not possible due to #4, it also needs special care in how the username is shown:
first edit:
edited by x
second edit:
edited by x and y
third edit and more:
edited by x, y and z
if username doesnt fit:
edited by multiple people
namely this part is problematic as it doesnt show who edited the message, in this case the editors could instead be appended to the end of the message