Remove extra commands from default generator flow

[pcostesi]

Rely on subgenerators/commands to get that info. We're keeping the
options in app.js so they transfer to subgenerators.

Fixes #10.

Tests:

• created a new folder and ran "yo office" inside. Selected the default options, save for "task pane". Result: does not hang.
• created a new folder and ran "yo office:taskpane" inside. Ran with default options. Result: does not hang.
• created a new folder and ran "yo office:mail" inside. Ran with default options. Result: hangs.
• created a new folder and ran "yo office" inside. Ran with default options, save for "mail". Result: hangs.
• created a new folder and ran "to office:content". Ran with default options. Result: does not hang.

[msftclas]

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[jthake]

Merged into Dev and under release 0.6.5 plans