Adding the concept of "transactions" to the MWS front end.

A transaction is just a collection of input & output files and the Moab
jobs that read or write those files.  When a user opens a transaction,
the system will create a directory where the user can upload files (job
scripts for example) and where the user's jobs can write output files
(which the user can then download).  While the transaction is open, the
user can submit one or more jobs to MWS that use those files.  The files
(and the directory they live in) will be deleted when the user closes
the transaction.