Clarify "Use default" in Save output (to describe what it does)

[BigRoy]

Problem

The Use default behavior under the Save options (in IOPlugin) doesn't describe how it behaves. The question from artists is: "What is default?"

Proposal

I'd like to propose two solutions.

1. Remove the Use default option.
2. Add a tooltip message to the checkbox.

1. Remove the use default option

With the implementation of render tokens in #28 we can remove the default and maybe instead allow users to define their own "dynamic default" through render tokens. This way it's much less hardcoded and is clear to the user what it does.

2. Add a tooltip message to the checkbox

This would clarify on mouse-hover what it does. Most artists are trained to request additional information from UI items by hovering over them, though in many scenarios it's not instantly clear what the UI item does. By implementing a tooltip we can add some clarification. It's debatable on how good of a solution this is UX-design wise.

Let's discuss what solution would be the best fit. I'm currently thinking about proposal 1.

[aardschok]

As the Use default option has been removed we might want to implement the tool tip for the Save option anyways.

[BigRoy]

Some notes regarding the current UX (User experience):

1. Regarding tooltips for save, I believe that will help! So +1.
2. I think when Save is disabled we can still hide the filename and browse field because then they are truly redundant.
3. Currently the placeholder text for the filename field is Select a directory which is confusing in itself; it's not about selecting a directory, but about defining a filename or full file path. I believe for this we can "learn" from the render settings filename box. That one has: (not set; using scene name) Would that make more sense?
4. Similarly, learning from the filename field in the render settings, we could add a tooltip that describes the right-mouse button context menu for render token functionality: Right click in the textfield to insert tokens.

[BigRoy]

@aardschok

2. I think when Save is disabled we can still hide the filename and browse field because then they are truly redundant.

Should we still implement this?

Point 1, 3 and 4 should already be implemented.