TweetUtils: Add utility method to process tweet array

Currently, parsing, allocating and then adding tweets(or rather their
GtkWidget counterparts, i.e. TweetListEntry) takes ~0.2s, which makes
the block.
This commit makes pretty much everything worse, but it improves THAT.
YAY.
ITimeline: Remove the tweet_type parameters
Tweet: Remove `type` and the corresponding constants
TweetUtils: Remove unneeded variable in work_array
ListStatusesPage: Remove unused load_newer
TweetUtils: Fix indentation
ListStatusesPage: Use TweetUtils.work_array
ProfilePage: Use TweetUtils.work_array
ListStatusesPage: Also use work_array in load_older
Merge branch 'no-stutter'