Integration with static analyzers

[osma]

We should set up static analyzers that monitor code quality. These tools can be integrated directly with GitHub so that they check each committed version.

We could use one or more of these tools: (even all of them if it's not too much work)

• Codebeat
• Scrutinizer
• Code Climate
• SourceClear

[osma]

Set up Code Climate: https://codeclimate.com/github/NatLibFi/Annif

[osma]

Set up Scrutinizer CI: https://scrutinizer-ci.com/g/NatLibFi/Annif/

[osma]

Set up Codebeat: https://codebeat.co/projects/github-com-natlibfi-annif-master

[osma]

Still need to add badges to the README.md, but I'll wait for the branch issue3 to be merged first to avoid conflicts.

[osma]

SourceClear seems different, it won't integrate directly with GitHub and their free plan seems limited to 10 scans a month. I think we can leave it out for now.