Fixed Image module tests. Added many critical todos:

- Config values are not casted to strings (despite promised).
- Config keys are not casted to strings (although promised, too).
- XML can be invalid and not parse-able for many reasons.
- Config keys are not validated/sanitized.
- config()->clear() should really be ->unset().
- Configuration must not be additionally cached by a module in any way (static cache / database cache).
- Some modules invoke drupal_alter() on configuration (e.g., image styles).
- Need a way to list config object names/suffixes _after_ a specified prefix.
- Need a way to determine whether a config object exists.
- Some modules might have a valid use-case for retrieving/listing config objects using a wildcard within the name (instead of only searching by prefix).
- The key of a retrieved value is unknown; since you only get the value.  Configuration values (or sub-values) may be passed forward to another function/callback, and thus, that function no longer knows about the key of the value. (unless the key is contained in the value, which is a very very wonky duplication)
- Config keys must not contain periods (within a specific key).