SysInfo: add GetOsVersion() function for all platforms
SysInfo: add GetOsPrettyNameWithVersion() function for all platforms
SysInfo: add GetModelName() function for all platforms (currently only iOS and Android return meaningful values)
Application: unify startup log strings for all platforms
SysInfo::GetUserAgent: included win32 refactored part, updated code to use new functions
Rename kernelVersion->osVersionInfo, SYSTEM_KERNEL_VERSION -> SYSTEM_OS_VERSION_INFO
Old name was incorrect as XBMC provide much more information than just kernel version
SysInfo: add GetManufacturerName() function for all platforms (currently only Android and Darwin return meaningful values)
Startup log: use manufacturer name
SystemInfo: cleanup: remove unused platform-specific functions
SysInfo: cleanup: remove not used now GetOsNameWithVersionInfo()
SysInfo: remove not used now platform-specific GetLinuxDistro()
SysInfo: remove not used now GetUnameVersion(), function result was inconsistent across platforms
SysInfo: remove not used now platform-specific GetAndroidVersionString() and GetAndroidDeviceName()
SysInfo: remove not used now platform-specific GetUAWindowsVersion()
SysInfo: cleanup: remove ancient declared only functions