Fix 39

# Changes

- `irc.yaml` is now the configuration file
  - it contains all information that `settings.txt` and `settings.py` used to
  - PyYAML module is used to parse this file at startup in `main.py`, and is passed to the `IRCBot` at creation
- `IRCBot` class is now instantiated inside of `main.py`
  - allows abstraction of settings file (won't have to change `core.py` every time settings change/need to be read differenty)
  - allows steps to happen between `__init__` and `run` easier/more intuitively
- `.idea` directory added to `.gitignore` (it's a PyCharm project directory)
- `settings.py` has been removed as it is now unnecessary