Code cleanup

Using some code inspector tools, the following changes are made:

- A reference to an `\ArrayAccessor` interface which should in fact be a `\Phinx\Config\Config` object (references to methods on `Config` are made to the objects, so `\ArrayAccessor` is insufficient as a type hint).
- Removes unused `use` statements.
- `void` methods do not return anything.
- Adds `@throws` statements to PHPDoc where missing.
- Adds better `@param` PHPDoc statements (e.g. specifying in PHPDoc the type of array being returned)
- Corrects invalid PHPDoc params.
- Corrects undefined variable errors.
- Removes a few unused variables.
- Removes unnecessary fully-qualified namespaces.

Only a few of the changes correct actual errors in the code (e.g. undefined variables), but this cleanup makes development with a modern IDE much easier.