Refactor job execution table

[dfaller]

This is a major refactoring effort to split the job_exe table into multiple tables for scalability.

Key changes:

• job_exe table is being split into multiple tables to improve scalability; job_exe tables will be insert only (no updates)
• queue table will hold input file meta-data to remove need for command argument refresh and to support future features like providing input file meta-data to jobs