Preferences dialog should better fit HIG

Hi,

I have some suggestion to improve the preferences dialog in openshot.

First, why do not use normal GtkNotebook for the category ? It save place and it's more consistent with the rest of the desktop.

Why do not make the theme selection instant apply instead of showing a preview ? That's recommended by HIG and save place too.

The project type should not appear in the preference dialog, it would be better to remove it. It should be plain text by defaut and if it's binary, it should be handled by code.

The history max step option should use a gtkspinbutton.

The big button in the profiles category is ugly, why do not embed directly the profile window in the preference window ?

I attached a patch who made some thing i suggested. It work great and make the code simplier. What i plan to do is removing the apply and cancel button and replace them with a close button and save changes when the focus change.

Tell me what you think !

Thanks.