examples/lle: Set missing properties of the ListListEntry
Revert "list-list-entry: Add info button"

This reverts commit ab2dc99477fd72a4c14dc2afb406f08804438b50.
TweetInfoPage: Remove follow button completely

It wasn't shown for quite some time so let's remove the entire logic
behind it.
Utils: Add usable_json_value

We can never do anything with null values in our json data, so add a
utility function to find out if a particular value exists AND is
non-null.
TweetInfoPage: Don't access the reply ID of non-reply tweets

If a tweet is coming from a protected account and is not a reply to
another tweet, the reply_to_status_id field will be set to null.

See #249