Crash on initial loading

Using system-provided Mono 6.8.0.105, the game crash at the end of the initial loading phase, right before showing the game menu, with the following trace:

[FMOD] d:\Jenkins\workspace\Ursa_SDL2\GSGE\GSGE\Code\Audio\AudioManager.cs:ln - 597 Unsupported file or audio format. Failed to create VO sound bank: Content/Audio/FMOD/Build/Desktop/VO.fsb
  at GSGE.AudioManager.LoadVoiceBank () [0x0034a] in <160751e4f5c141ae8efac1285e76459f>:0
  at GSGE.AudioManager.Preload () [0x00021] in <160751e4f5c141ae8efac1285e76459f>:0
  at GSGE.Code.GUI.LaunchScreen+<>c__DisplayClassc.<MapLoad>b__9 () [0x00040] in <160751e4f5c141ae8efac1285e76459f>:0
  at System.Threading.Tasks.Task.InnerInvoke () [0x00012] in <12b418a7818c4ca0893feeaaf67f1e7f>:0
  at System.Threading.Tasks.Task.Execute () [0x00000] in <12b418a7818c4ca0893feeaaf67f1e7f>:0

To work around it, we use the shipped binaries Mono build instead of system-provided Mono.
