Navigation - Fix serialization error

Navigation - Fix serialization error

Overview
--------

The navigation subsystem stores per-user data in the table
`civicrm_setting`.  Most access to this table goes through
`CRM_Core_BAO_Setting` or `Civi\Core\SettingsBag`.  However, certain
edge-cases produce a warning about a serialization error because
`CRM_Core_BAO_Navigation` does not participate.

Before
------
`CRM_Core_BAO_Navigation::resetNavigation()` generates malformed
records which cannot be read via `CRM_Core_BAO_Setting` or
`Civi\Core\SettingsBag`.

After
-----
`CRM_Core_BAO_Navigation::resetNavigation()` generates better records.