[IMP] Better versality for new and edit commands

[arbaes]

none can be used as a bot command argument. What it changes:

new

• Allow creating role-reaction messages with only an embed message (introduced by [IMP] Make embeds optionnal as those can be hidden clientside #21)

edit

• Allow editing/removing individually the message body, the embed's title and the embed's description

[eibex]

Looks great, though I would add an explanation about these new arguments on line 178 for rl!new and line 304 (308 in the new code) for rl!edit.

Thanks a lot for all the help :)

EDIT: I will do that myself in the sqlite branch while I work on some other stuff.