Setup project structure for the future

[piotrmacha]

Changes:

• plugin/ directory with source code moved to project root
• NH::Bass classes moved to src/NH/Bass
• Removed all empty includes from gothic-userapi
• Game_* exports removed and replaced with direct hooks to be independent of Union 1.0 runtime
• Changed CGameManager::Init() patch hook to partial hook at the start of CGameManager::Run()
• Fixed setting up logger level from .ini options
• Additional CMake targets to build VDF and copy to folder
• Added BuildInfo with constants describing the build variables
• Change Union API linking to dynamic
• Upgrade dependencies