set column names for empty dataframe properly

[ccleung]

Tracker Ticket: https://quandl.atlassian.net/browse/AP-1780

Description:

• R-package was erroring out because if the data returned is empty form quandl response, it will have 0 columns and so we cannot rename the columns
• Fix this crash by setting an empty data frame ourselves, one that is initialized with x columns with no data
• Set the names of the columns properly for empty data response
• Default column type is now "character"

  Note to the reviewer:

  Note to QA:

• Ensure column names are set properly for data response (when there is no data in response, and when there is data)
  • no data example call: Quandl.datatable('ZACKS/FC', qopts.per_page=1, per_end_date='2016-10-10')
• Ensure column types are set properly in each scenario: you can verify the column types by doing this on the data frame: sapply(df, class) where df is obtained by df <- Quandl.datatable(...)
• R types: character, date, numeric
• https://www.quandl.com/api/v3/datatables/ZACKS/FC?<> BigDecimal, String, Integer, Dates

  Dependency(if any):

  Screenshot(if any):

[RaymondMcT]

:shipit:

[ccleung]

@RaymondMcT has informed me that the :shipit: (:shipit:) is synonymous with the 👍