Fix for issue #89: Add ctoSystem option to CLI, other CLI improvements

[jeromesimeon]

Issue #89

• Add --ctoSystem option to CLI
• Default system is base Accord Project one
• Refactor so system and user models are loaded consistently from disk or URL in the various commands
• Add info output when cicero get succeeds

Examples:

bash-3.2$ ./index.js get --ctoFiles https://models.accordproject.org/docusign/[email protected] --outputDirectory dsout 
./index.js get --ctoFiles https://models.accordproject.org/docusign/[email protected] --outputDirectory dsout 
13:26:55 - info: Loaded external models in 'dsout'.
bash-3.2$ ./index.js get --ctoSystem ./test/models/org.hyperledger.composer.system.cto --ctoFiles https://models.accordproject.org/docusign/[email protected] --outputDirectory dsout 
./index.js get --ctoSystem ./test/models/org.hyperledger.composer.system.cto --ctoFiles https://models.accordproject.org/docusign/[email protected] --outputDirectory dsout 
13:27:06 - error: Relationship transactionInvoked must be to an asset or participant, but is to org.hyperledger.composer.system.Transaction File './test/models/org.hyperledger.composer.system.cto': line 137 column 3, to line 138 column 3.