Sanitize all categories

[gandarez]

This PR implements the recent changes made to sanitization logic. Now all entity types must be considered for sanitization. One important change is the HIDDEN text will only have extension for FileType.

#98

[dron22]

Ok, the amount of tests is a little overwhelming. I think we can make this a little bit more concise:

1. Let's only test WithSanitization with heartbeat of type file. This test should basically verify, that Sanitize is integrated correctly. No need to test different cases here.
2. I used a test helper function testHeartbeat() to avoid setting up the heartbeat repeatedly. Let's have 3 of these: testHeartbeatFile, testHeartbeatApp and testHeartbeatDomain.

This way there will be less code. I am a lazy guy 😉

[dron22]

This looks like a nice PR to review!

Can you make sure you perform git rebase -i --autosquash origin/master and force push before merging? These fixup commits should only be there during review. We do not want them in the history...