Services Registration

[cdcarter]

Critical Changes

Now enforcing services and service required fields. Any services that you use in a custom task must now be defined in cumulusci.yml services.

New commands for interacting with services:

cci services list
cci services show github
cci services connect github

Changes

Issues Closed

#224 - Define services and schema

[cdcarter]

not quite ready to merge, i want servicesconfig to verify itself. but. this handles the cli side of things nicely.

[cdcarter]

• _validate_service() on ServiceConfig
• test cases for keychain and config
• cherrypick out commits that are bugfixes on other things
• documentation in the tutorial
• docstrings
• is the multicommand the best way to get dynamic options?
• can I use some of jlantz's magic to access the attribute schema more easily?

[jlantz]

This change looks great to me. I can do the doc changes pretty easily after merging. Are there other bug fixes you want to load into the branch before merge or do you just want to handle those as separate PRs?

[cdcarter]

671ecd7 and 3a303c1 are the two kind of unrelated changes that should at least be noticed, but everything is here in this PR!