initial support for obtaining a MySQL database on Amazon's cloud (Issue #60)

- new shell command that allow you to create a small (ie. free) DB instance (MySQL) on amazon cloud using the same credentials/aws account created for MTurk
- can switch between local SQLLite database and cloud-based system
- switch between different RDS instances and different databases in the cloud
updating database info in README.md
ability to change AWS region
maybe no longer need to scare people with warnings about database issue given the AWS RDS support
a little reorganizing of the file
get current DB config
starting to lay out skeleton for new command structure
Added completion to server command

Changed command names to reduce number of server commands with same starting letter, and added space to end of completions for easier two word completion.
added worker and hit completion
added help method to server command
added worker commands and worker help, started deprecating old commands.
Deprecated old hit commands

All subsumed commands should be deprecated now. Also changed amt_services to treat None argument differently in extend_hit
reorganizing: put all deprecated commands together
added more help messages
Added persistent command history
fixed check_balance bug
fix to install shell help files

the shell help files weren't being copied via the setuptools script resulting in an error message
ignore history file

just to be safe
loads .psiturk_history into new session if it has commands
Merge remote-tracking branch 'origin/shell_reorg' into aws_rds

Conflicts:
	psiturk/psiturk_shell.py
	psiturk/version.py