Su-15 Flagon mod v1.0 support (#345)

* Su-15 Flagon mod v1.0 support

Implemented support for Su-15 Flagon mod version 1.0 by Marco1985_IT.

* Replaced the external fuel tanks with gunpods in Su-15 loadouts and added gunfighter: true

resources/units/aircraft/Su_15.yaml

@@ -0,0 +1,20 @@
+description:
+  "The Sukhoi Su-15 (NATO reporting name: Flagon) is a twinjet supersonic interceptor
+  aircraft developed by the Soviet Union. It entered service in 1965 and remained one
+  of the front-line designs into the 1990s."
+introduced: 1965
+manufacturer: Sukhoi
+origin: USSR/Russia
+price: 12
+role: Interceptor
+max_range: 200
+gunfighter: true
+variants:
+  Su-15 Flagon-A: {}
+kneeboard_units: "metric"
+tasks:
+  BARCAP: 360
+  Escort: 360
+  Fighter sweep: 360
+  Intercept: 360
+  TARCAP: 360

resources/units/aircraft/Su_15TM.yaml

@@ -0,0 +1,23 @@
+description:
+  "The Sukhoi Su-15 (NATO reporting name: Flagon) is a twinjet supersonic interceptor
+  aircraft developed by the Soviet Union. It entered service in 1965 and remained one
+  of the front-line designs into the 1990s. The Flagon-A was followed in December 1971
+  by the Su-15TM (NATO Flagon-E), with the improved Taifun-M radar (NATO Twin Scan) 
+  and provision for UPK-23-250 gun pod or R-60 (AA-8 Aphid) short-range air-to-air
+  missiles."
+introduced: 1971
+manufacturer: Sukhoi
+origin: USSR/Russia
+price: 12
+role: Interceptor
+max_range: 200
+gunfighter: true
+variants:
+  Su-15TM Flagon-E: {}
+kneeboard_units: "metric"
+tasks:
+  BARCAP: 370
+  Escort: 370
+  Fighter sweep: 370
+  Intercept: 370
+  TARCAP: 370