Error handling

[SaschaAdler]

There are a lot of things in Kivik's codebase that can throw uncaught exceptions. These exceptions should be caught, logged, and the code should gracefully fail accordingly.

• YAML.parse can't parse the RC file
• <deployment> does not refer to a key in the RC file
• Docker errors (src/Container.js)
• require, fs.read*
• nano can't communicate with couch
• couch forbids a nano request
• Things are stopped before they're started, deployed before they're loaded, etc.

[SaschaAdler]

I removed a couple of tasks because Kivik no longer invokes ajv directly. #50

[SaschaAdler]

I'm confident other things are sorted out reasonably well, although I'll have to test them (#57)