Sorting by Series Title ignores articles

Added DB migration to add sortTitle column.
I've changed the UI to sort by the sortTitle instead of title on all views. the SeriesCollection views sort in the UI-code, the rest are paged views so sort in the database.

Additionally I've changed a bit of logic regarding Next Airing.
Normally those without a Next Airing would show up unsorted at the end of the list.
So I've added a secondary sort by Previous Airing. Which means recently aired series will be listed first (after the Next Airing items, of course)
This means a really old show will be at the bottom of the list.