Add support for watchlists

[Amodio]

Fix #81

Watchlist(s):
#2: test ! (default=True)
#1: Favorites (default=False)
Created a new watchlist with id: #3
Adding symbol 'AAPL' to watchlist #3
Content of created watchlist (My Watchlist #3): [
  {
    "watchlist_id": 62715860,
    "sec_type": 1,
    "symbol": "AAPL",
    "quantity": 0,
    "last": 259.78,
    "bid": 259.43,
    "ask": 259.79,
    "vol": 26373084,
    "change": -1.05,
    "change_percent": -0.4,
    "day_gain_amount": 0,
    "unit_cost": 0,
    "cost": 0,
    "gain_amount": 0,
    "gain_percent": 0,
    "bidsize": 448,
    "asksize": 100,
    "high": 262.13,
    "low": 259.55,
    "close_price": 260.83,
    "open_price": 261.08,
    "update_time": "21:33:38 am"
  }
]
Deleted watchlist #3.

[Amodio]

Note: new files are not tracked due to the .gitignore, which currently ignores everything:

$ cat .gitignore 
# Created by venv; see https://docs.python.org/3/library/venv.html
*

$ git add firstrade/watchlist.py 
The following paths are ignored by one of your .gitignore files:
firstrade
hint: Use -f if you really want to add them.
hint: Disable this message with "git config set advice.addIgnoredFile false"