Filter in insert_with_lock_in. Fixes scrolling.

I got tired of messages getting pushed out of the queue by spam, so I
decided to change things up and hook in to insert_with_lock_in instead.
Now the line counter is based on the currently displayed messages and
scrolling works properly.
Fix initialize_filter() being called prematurely

Sometimes CurrentChat isn't finished loading before we call
initialize_filter() so we'll check to see if the loading_spinner is
hidden before calling it. Fixes #28
Merge pull request #26 from ajhodges/master

Filter in insert_with_lock_in, fix scrolling. Fix init.