Fix two issues

* https://github.com/saintnicster/FTBLaunch/commit/e13f364890893e7a530203bf08fa3d742f61c63a
[Console log](http://pastebin.com/qTHVxj3J)
> Caused by: java.lang.ClassNotFoundException:
>        at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
>        at java.security.AccessController.doPrivileged(Native Method)
>        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
>        at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
>        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
>        at java.lang.ClassLoader.loadClass(ClassLoader.java:247)

Fix - only add additional arguments to the list if they aren't blank (strlen != 0)
* * *
* LauncherStyle file not opening/saving correctly on OS X/*nix.  Same basic issue as PR #509.
[Console log (different)](http://pastebin.com/Pten1Wkw)
>[15:26:20] [WARN] FileOutputStream.open:-2->LauncherStyle.load:76: Could not save style: java.io.FileNotFoundException: /Users/nickfajardo/ftb/Direwolf20/Library/Application Support/ftblauncher/launcher_styles/defaultStyle.cfg (No such file or directory)
>		java.io.FileOutputStream.open(Native Method)
>		java.io.FileOutputStream.<init>(FileOutputStream.java:194)
>		java.io.FileOutputStream.<init>(FileOutputStream.java:145)
>		net.ftb.data.LauncherStyle.load(LauncherStyle.java:74)
>		net.ftb.data.LauncherStyle.load(LauncherStyle.java:46)
>		net.ftb.data.LauncherStyle.<clinit>(LauncherStyle.java:30)
>		net.ftb.util.StyleUtil.loadUiStyles(StyleUtil.java:9)
>		net.ftb.mclauncher.MinecraftFrame.<init>(MinecraftFrame.java:33)
>		net.ftb.mclauncher.MinecraftLauncher.main(MinecraftLauncher.java:194)

[LauncherStyle.java#L23](https://github.com/Slowpoke101/FTBLaunch/blob/master/src/net/ftb/data/LauncherStyle.java#L23)
Fix - Cache the System.getProperty("user.home") in a class-wide static method on OSUtils and use that in OSUtils.getDynamicStorageLocation().  This should fix any other instances where files may need to be read/written (after the MinecraftLauncher class has been called)