Improve expedition GS rate prediction
Improve expedition GS rate prediction

Implement a new formula for predicting expedition GS rate, based on the
one datamined from Kancolle Kai.

Resolves: #1951

Tibo442/KC3Kai,sinsinpub/KC3Kai,DynamicSTOP/KC3Kai,Yukinyaa/KC3Kai,reinforce/KC3Kai,kololz/KC3Kai,Adrymne/KC3Kai,kololz/KC3Kai,DynamicSTOP/KC3Kai,reinforce/KC3Kai,sinsinpub/KC3Kai,Tibo442/KC3Kai,dragonjet/KC3Kai,Adrymne/KC3Kai,Yukinyaa/KC3Kai,dragonjet/KC3Kai,reinforce/KC3Kai,sinsinpub/KC3Kai,Tibo442/KC3Kai,DynamicSTOP/KC3Kai,kololz/KC3Kai,KC3Kai/KC3Kai,Adrymne/KC3Kai,KC3Kai/KC3Kai,KC3Kai/KC3Kai