[linkchecker] Link Checker

# Summary

Check links

# Project URL

https://www.drupal.org/project/linkchecker

# Where is the code?

https://www.drupal.org/project/linkchecker

# Estimated completion date

# Dependencies

# Who's doing the port?

# What help do they need?

# D8 roadmap

#2422035: [META] Porting module to Drupal 8

# Background and reference information

(Links to any other helpful information, documentation, etc.)