Added no output file module

Issue addressed

The pattern for NekMesh requires an explicit output file to be provided by the user even for statistic or no output modules like the star ccm+ module writelabelsonly.

This was raised a while ago by issue #288 .

Proposed solution

In the FieldConvert, if the output file name or file extension is stdout, no file will be output. (This file will not be printed on the screen either.) This feature can be introduced to Nekmesh.

Implementation

We introduced a new OutputModule OutputStdOut that outputs nothing.

Tests

Checklist

• Added blank output module
• Added nooutput input module
• Added module check in base class
• Changelog is updated.
• Changes are tested.
• Newly added files are correctly formatted.