Code refactoring

[valeriobelcastro]

This PR is to refactor code structure. With the new structure there are:

• bot package: which contains the default bot implementation and is extended by the Fungiforme implementation. It also contains the logsetup module.
• fungiforme package: containing fungiforme bot implementation
• fungiforme.commands package: containing all commands implementations according to discord.py Cog pattern
• fungiforme.event_listeners package: containing all event_listeners implementations according to discord.py Cog pattern
• fungiforme.tasks package: containing all tasks implementations according to discord.py Cog pattern

fix #49