When creating a new CTF, check if a CTF with the same name already exists

[mklarz]

The bot errors out a CTF with the same name exists, should perhaps be unique in the DB as well? Append a number to the CTF name?

2021-04-16 13:09:10,309:ERROR:bot: Ignoring exception in command create
Traceback (most recent call last):
  File "/usr/local/lib/python3.9/site-packages/discord/ext/commands/core.py", line 85, in wrapped
    ret = await coro(*args, **kwargs)
  File "/home/bot/ctfs.py", line 39, in create
    messages = await respond_with_reaction(
  File "/home/bot/ctfs.py", line 332, in respond_with_reaction
    msg = await chan.send(msg)
AttributeError: 'NoneType' object has no attribute 'send'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/usr/local/lib/python3.9/site-packages/discord/ext/commands/bot.py", line 903, in invoke
    await ctx.command.invoke(ctx)
  File "/usr/local/lib/python3.9/site-packages/discord/ext/commands/core.py", line 859, in invoke
    await injected(*ctx.args, **ctx.kwargs)
  File "/usr/local/lib/python3.9/site-packages/discord/ext/commands/core.py", line 94, in wrapped
    raise CommandInvokeError(exc) from exc
discord.ext.commands.errors.CommandInvokeError: Command raised an exception: AttributeError: 'NoneType' object has no attribute 'send'
2021-04-16 13:09:10,312:INFO:bot: Error occured with: create
Command raised an exception: AttributeError: 'NoneType' object has no attribute 'send'