Make datafolder to appdata, and its linux equivalent

[nopara73]

No description provided.

[wintercooled]

I've done this with a service in Windows and Linux (and Mac) so am happy to pick this up at some point. In Windows the folder location varies by which OS it is - so I've code I can re-use here to handle this.

[nopara73]

Sounds good. Just pay attention not to conflict with Electron's stuff. It messes into the appdata folder.

For reference, this is how Stratis and NTumbleBit is going it:

        /// <summary>
        /// Finds a location of the default data directory respecting different operating system specifics.
        /// </summary>
        /// <param name="appName">Name of the node, which will be reflected in the name of the data directory.</param>
        /// <param name="network">Specification of the network the node runs on - regtest/testnet/mainnet.</param>
        private void SetDefaultDataDir(string appName, Network network)
        {
            string directory = null;

            if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
            {
                var home = Environment.GetEnvironmentVariable("HOME");
                if (!string.IsNullOrEmpty(home))
                {
                    this.Logger.LogInformation("Using HOME environment variable for initializing application data.");
                    directory = Path.Combine(home, "." + appName.ToLowerInvariant());
                }
                else
                {
                    throw new DirectoryNotFoundException("Could not find suitable datadir");
                }
            }
            else
            {
                var localAppData = Environment.GetEnvironmentVariable("APPDATA");
                if (!string.IsNullOrEmpty(localAppData))
                {
                    this.Logger.LogInformation("Using APPDATA environment variable for initializing application data.");
                    directory = Path.Combine(localAppData, appName);
                }
                else
                {
                    throw new DirectoryNotFoundException("Could not find suitable datadir");
                }
            }

            if (!Directory.Exists(directory))
                Directory.CreateDirectory(directory);

            directory = Path.Combine(directory, network.Name);
            if (!Directory.Exists(directory))
            {
                this.Logger.LogInformation("Creating data directory...");
                Directory.CreateDirectory(directory);
            }

            this.DataDir = directory;
        }

[nopara73]

Done.