Reapply "east slavic cultures+traditions+innovations (wip)"

This reverts commit c338758064.

common/culture/innovations/N3OW_cultural_innovations.txt

@@ -0,0 +1,26 @@
+@longboats = "gfx/interface/icons/culture_innovations/innovation_longboats.dds"
+
+innovation_river_tradefleets = {
+	skill = stewardship
+	group = culture_group_civic
+	culture_era = culture_era_early_medieval
+	region = world_europe_east_russia
+	icon = @longboats
+
+	character_modifier = {
+		embarkation_cost_mult = -0.5
+		diplomatic_range_mult = 0.2		
+	}
+
+	custom = unlocks_sailable_major_rivers
+	parameters = {
+		trade_ports_stationed_maa_bonus = yes
+		trade_ports_enabled_for_tribals = yes
+	}
+	flag = global_regional
+	flag = early_medieval_era_regional
+	
+	ai_weight_for_fascination = {
+		value = 100
+	}
+}