Improves output logging and fixes some bugs

Fixes an error caused by the BuildTools directory not being created
Creates functions for writing to files in CommonFunctions
Adds some more error info to the log when BuildTools fails to download
Fixes some typos
Makes sure all visible text is logged

src/main/java/net/knarcraft/minecraftserverlauncher/userinterface/GUI.java

@@ -44,6 +44,20 @@ public interface GUI {
      */
     void showMessage(String message);
 
+    /**
+     * Logs a message to the logfile
+     *
+     * @param message <p>The message to log</p>
+     */
+    void logMessage(String message);
+
+    /**
+     * Logs an error to the logfile
+     *
+     * @param error <p>The error to log</p>
+     */
+    void logError(String error);
+
     /**
      * Asks the user for a directory as a file object
      *