Update MFLinkedInComposeViewController to intelligently prepare the post based on the items in the activityItems array. Update Demo app to pass required LinkedIn parameters to activityItems array and meet Library Specifications.

Created the following Library specifications (for library clients):
“When initializing the UIActivityViewController with it's initWithActivityItems:applicationActivities: method, the number of objects passed to the activityItems array MUST be [4] and the objects must be in the following order:
object at index 0: title    (Title of shared document)
object at index 1: description           (Description of shared content)
object at index 2: submitted-url         (URL for shared content)
object at index 3: submitted-image-url   (URL for image of shared content)

 SPEC NOTE 1: the "submitted-url" is required by the LinkedIn Share API, if you don't provide this property, http://www.linkedin.com will be used by the library, so make sure you provide one at activityItems index 2.

 SPEC NOTE 2: If there is one or two properties out of these four (with exception of "submitted-url") that you don't intent to use for your project, just pass an instance of the NSNull class (since an Objective-C collection doesn't take a nil value) to the activityItems array.