add parameters to config

[ScottABrown]

This commit adds parameters including a no-prompt option for config(), to facilitate Docker container setup.

• This makes the current prompted settings configurable by options to "aardvark config".
• I think the aardvark-role, swag-bucket and db-uri are likely more common, so they have short options available. num-threads, phantom and no-prompt only offer long options.
• I suspect the region and a couple other config settings should be configurable but that can be a separate commit. I considered '-r' as short for aardvard-role but wanted to reserve it for the possibility of a region option, so I used '-a' as short for aardvark-role instead.
• For consistency/simplicity, to allow a no-prompt option without requiring some parameters be specified this adds nominal default values for the swag bucket name and the aardvark role: DEFAULT_SWAG_BUCKET = 'swag-data' and DEFAULT_AARDVARK_ROLE = 'Aardvark'.
• The config() function now raises an exception if the phantomjs executable can't be located at config() time and isn't specified either by parameter or user input.
• Fixed some formatting issues in the config file writes (braces in format strings and a couple of newlines).

[mcpeak]

Great work, thanks!