Refactor error collection and display

[jadefish]

Problem

The current process for aggregating and displaying errors from server responses is not capable of handling deeply-nested error structures (e.g. nested Dry validation schemas, arrays).

Additionally, only client-side errors are visually associated with their failing element.

Context

The current implementation yields the following behavior:

• Nested error structures result in displaying [object Object] in the nearest error <div> element.
• All errors collected from server responses are displayed in the nearest error <div> element instead of close to or within each error's associated element.

Proposed solutions

• All error collection and display should be capable of handling errors structures of arbitrary depth.
• Errors collected from responses should be displayed alongside their associated element.
• Page-level errors (the nearest error <div> element behavior) should be used only when an error cannot be associated with an element (e.g., errors describing a loss of network connectivity).