Add Google Finance Data Source: diversify data sources (enhancement)

[helgasoft]

Library tidyquant is quite useful, but is hard-coded to Yahoo stock price data (see 'stockprice' in tq_get_util_1). Lately Yahoo stock price data has become somewhat unreliable.
A good enhancement would be to add Google as alternative data source, getSymbols.google is already available in quantmod, it would be just a matter of including it in code.

[mdancho84]

We agree. We are also adding alphavantager as well because of the yahoo debacle. Reliability is extremely important.

[mdancho84]

@helgasoft I've integrated getSymbols.google. Use `tq_get(get = "stock.prices.google") and it should return data from Google Finance.