Profanity filter: commands to customize whitelisted words

[snapcat]

Relevant files:
profanity_helper.py, bot.py
And possibly cogs/wordfilter.py if you decide to use a cog.

• Command to whitelist a word
• Command to remove a word from the whitelist
• Command to save newly whitelisted words
• Command to load saved whitelist from file (see profanity_helper.py -- started but not finished)
• Command to clear saved whitelist (clear file)