Ukrainian, Russian and US assets in Frenchpack

Added unit yamls for M551 Sheridan, T-62 and T-64BV from Frenchpack mod.

resources/units/ground_units/SHERIDAN.yaml

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+class: ATGM
+description: The M551 Sheridan AR/AAV (Armored Reconnaissance/Airborne Assault Vehicle)
+  is a light tank developed by the United States and named after General Philip Sheridan,
+  of American Civil War fame. It was designed to be landed by parachute and to swim across
+  rivers. It is armed with the technically advanced M81/M81 Modified/M81E1 152 mm
+  gun/launcher, which fires both conventional ammunition and the MGM-51 Shillelagh guided
+  anti-tank missile.
+introduced: 1966
+manufacturer: General Motors, Cadillac Motor Company
+origin: USA
+price: 16
+role: Light Tank
+variants:
+  M551 "Sheridan": {}

resources/units/ground_units/T62.yaml

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+class: Tank
+description: The T-62 is a Soviet main battle tank that was first introduced in 1961.
+  As a further development of the T-55 series, the T-62 retained many similar design
+  elements of its predecessor including low profile and thick turret armour. In
+  contrast with previous tanks, which were armed with rifled tank guns, the T-62 was
+  the first production tank armed with a smoothbore tank gun that could fire APFSDS
+  rounds at higher velocities. 
+introduced: 1961
+manufacturer: UralVagonZavod
+origin: USSR/Russia
+price: 19
+role: Main Battle Tank
+variants:
+  T-62: {}

resources/units/ground_units/T64BV.yaml

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+class: Tank
+description: The T-64 is a Soviet second-generation main battle tank, designed by
+  Kharkiv Morozov Machine Building Design Bureau in Ukraine, introduced in the early
+  1960s. It was a more advanced counterpart to the T-62; the T-64 served in tank
+  divisions, while the T-62 supported infantry in motorized rifle divisions. It
+  introduced a number of advanced features including composite armour, a compact
+  engine and transmission, and a smoothbore 125-mm gun equipped with an autoloader
+  to allow the crew to be reduced to three so the tank could be smaller and lighter.
+  In spite of being armed and armoured like a heavy tank, the T-64 weighed only 38
+  tonnes (42 short tons; 37 long tons).
+introduced: 1966
+manufacturer: Kharkiv
+origin: USSR/Russia
+price: 19
+role: Main Battle Tank
+variants:
+  T-64BV: {}