add plugin templating feature

[edaniszewski]

a plugin templating feature would make it easier for new plugin developers to get started. see the synse v3 spec for more.

[GuessWhoSamFoo]

Existing work in branch:

https://github.com/vapor-ware/synse-cli/tree/v3/templating

• Address whether VCS information is needed in the metadata
• Find other potentially missing pieces of metadata like required dependency versions such as SDK or go
• Should the template scaffold a repo structure?