add options argument for chrome driver

[StephenDavidson]

Allows user to add custom options to the chrome browser.

[andrewsmedina]

@StephenDavidson thank you. Can you add a test?

[neilsh]

@andrewsmedina What would a test for this actually entail? It seems like this change is necessary for the existing tests to actually run properly.

[neilsh]

I guess there's also the larger question of whether it's preferable to have a general chrome_options object, or pass in separate args for individual options like the current/conflicting code does:

splinter/splinter/driver/webdriver/chrome.py

Lines 17 to 33 in ed21fb5

	def __init__(self, options=None, user_agent=None, wait_time=2,
	fullscreen=False, incognito=False, headless=False, **kwargs):
	options = Options() if options is None else options
	if user_agent is not None:
	options.add_argument("--user-agent=" + user_agent)
	if incognito:
	options.add_argument("--incognito")
	if fullscreen:
	options.add_argument('--kiosk')
	if headless:
	options.add_argument('--headless')
	options.add_argument('--disable-gpu')