Improve error messages

[antond-weta]

Each level of the tool should only have the info in the error messages relevant to that level.

Here is an example of the issue. When using the rawtoaces_util library, calling ImageConverter.process_image() prints out this:

ERROR: file "/path/to/the/output/file.exr" already exists. Use --overwrite to allow overwriting existing files. Skipping this file.

This is incorrect, because there is no --overwrite parameter anywhere but the command line tool.
The error message from the ImageConverter should instead suggest using ImageConverter.settings.overwrite = true and set some kind of status code, upon receiving which the higher level code could elaborate the error message further, say by suggesting using --overwrite in case of the command line tool.

Suggested solution:

• Each class which has methods returning bool should also have a status property, which would hold the latest call's error code.
• Each instance of reporting an error to the user should be providing only the relevant info, not assuming the higher level use case.

[jojoGits]

Hello! I'm keen to help with this

[jojoGits-Weta]

Hello! Can you please assign this to my new weta github?

[antond-weta]

Hello! Can you please assign this to my new weta github?

done!