Add a script to generate screenshots for visual validation

[berntpopp]

Add a script that will generate screenshots of the variants' alignment in the IGV browser so that it can be validated. This should be done for all the variants passing filtering. The screenshot should include at least one control.

TODO:

• check for existing implementations and tools
• check if IGV is suitable for this task
• check what scriping language to use
• decide for a format of the screenshots
• decide for a file naming convention
• decide for a folder structure
• Implement the script

[berntpopp]

Duplicate of #32