Fixed issue #9 to automatically sort the content object list by status

For published list, the content objects are sorted by latest published
time by default. For pending list, the content objects are sorted by
latest submission time by default.
Fixed issue #8 to allow search content objects by parentId parameter

This feature allows to search content objects by passing in "parentId"
parameter. It helps to create individual pages or API responses that
limit the result to be under a parent content object.