Add the ability to turn off image pulling.

Current situation:
* PodStatus is capitalized.
* Status.Status is lowercase.
* StatusReasons are lowercase, with underscores.
* CauseTypes are Java-style camelCase.

I haven't seen any JSON-based APIs that use all uppercase. They use some flavor of camel case or all lowercase with underscores. I also find all uppercase excessively attention-grabbing and space-consuming in the case of variable-width fonts.

Using Java-style camelCase makes string constants look like json fields. Using Go-style makes them look like types, which emphasizes their static nature and similarity to constants represented as structs. It also makes them more readable. We're going to be displaying status values, causes, reasons, etc. in the CLIs and UIs.

Example:
* `fieldValueInvalid`
* `FieldValueInvalid`
* `field_value_invalid`
* `FIELD_VALUE_INVALID`

Decision: Go-style CamelCase.