Remote file download patches.

[Foxcapades]

Changes:

• Update raml and container core to include and use 424 status responses
• Add cleanup method to trim user inputs (only relates to this change in that i found the lack of cleanup via an unexpected error for a url value with a leading space)
• Relocate DatasetPostRequest mixin function to the appropriate mixin function file.
• Handle 3xx redirects for given URLs including http -> https upgrades.
• Added error handling and responses for different possible failure cases to provide users with more informative messages.