Modified the start and stop transaction algorithms

Updated StartRemoteTransaction and StopRemoteTransaction to use the new
web API.  Also updated the cookie handling code in RemoteJobManager

Refs #7769
Changes to the HTTP POST function

Couple of minor changes to make POST requests work properly:
1) Need a blank line before the start of the data in multi-part mime
data
2) Separate file data from other data (by using a second PostDataMap
reference) because it needs to be handled a little differently in the
mime encoding

Refs #7769
Convert the upload and download algorithms to the new web API

Refs #7769
Update the Doxygen comments for the upload algorithm

Refs #7769
Add the Authenticate algorithm

Refs #7769