Update 7.0 stats added

Added stats for update 7.0. Interestingly, the player base tracked played far less battles during the update compared to the previous update despite the update interval being very long due to the WG release schedule.

Stats per Tier / Tank type

In addition I have added stats for tank types per tier. The other pages show only top 10/20 tanks per graph, but these pages list every tank of type at the tier.

plot of chunk fig_tanks_tier8_heavy_RelativeWR