Implemented writing vendor credentials to Java .properties file.

The latest Auto-Ingest tool no longer accepts username and password on the
command line; in their place, it takes the path to a Java .properties file
containing "userID" and "password" keys.

Added a "path" property to VendorFile to expose the path of the vendor file.

Added "credentialsFilePath" property to Vendor class.  The credentialsFilePath
is created by dropping the .plist extension of the corresponding VendorFile
path and adding .properties.  Vendor's -prepare method now checks for the
credentials properties file and creates it if missing.

Changed initialization of AutoingestionJob to replace the username and
password arguments with the credentialsFilePath from the Vendor.
Fixed mistake in creation of credentials properties file.

Was adding ".properties" extension, which resulted in "Vendor..properties"
files.

Made writing of credentials file happen every time Autoindigestion runs, to
make sure the credentials file has the latest username and password.
Made path to credentials .properties file relative rather than absolute.

The autoingestion jobs were failing with the message "Property file missing".
The AutoingestionJob class was creating the command line for the
Auto-Ingest tool using an absolute path to the .properties file with the
credentials; in manual testing of the Auto-Ingest tool I had used a relative
path.

Changed the init method of AutoingestionJob to build up a relative path
from the job's working directory (the directory where the particular report
being downloaded belongs) to the /Library/Autoindigestion/Vendors
directory.
Added -cleanUp methods to Tool and Vendor classes.

The Tool -cleanUp method calls -cleanUp for each Vendor.  The Vendor's -cleanUp
removes the credentials .properties file created in -prepare.
Updated "Security Considerations" section of man(1) page.

Noted the use of the .properties file for iTunes Connect credentials.
Also added man page links for launchd(8) and launchd.plist(5).