Update comments for Calendar ExtendedProperties.

 * {@link Calendars#MAX_REMINDERS} which is set by the Sync Adapter that owns

 * the given calendar. Reminders are specified in minutes before the event and

 * have a type.</li>

 * <li>The {@link ExtendedProperties} table hold opaque data fields used by the

 * <li>The {@link ExtendedProperties} table holds opaque data fields used by the

 * sync adapter. The provider takes no action with items in this table except to

 * delete them when their related events are deleted.</li>

 * </ul>

    /**

     * Fields for accessing the Extended Properties. This is a generic set of

     * name/value pairs for use by sync adapters or apps to add extra

     * name/value pairs for use by sync adapters to add extra

     * information to events. There are three writable columns and all three

     * must be present when inserting a new value. They are:

     * <ul>