Support SonarQube issue format

[junkpiano]

New Issue Checklist

• Updated SwiftLint to the latest version
• I searched for existing GitHub issues

Proposal

This is a new feature proposal.

Looking at #175 , SwiftLint was integrated by SonarQube plugin.
Now SonarQube 7.2 provides the way to import issues from the 3rd party analyzers.

• https://www.sonarqube.org/sonarqube-7-2/
• https://docs.sonarqube.org/display/SONAR/Generic+Issue+Data

So I added another reporter for SonarQube.
I conducted tests on my personal applications, and found my patch works fine and sents collect data.

It looks like this.

The difference is that the issue has SwiftLint tag besides the issue description.
We can continuously check our code violations on SonarQube.

On the other hand, there is a limitation. We cannot use character in the JSON we send.
I took a look at SonarQube code, where I got a java exception error.

https://github.com/SonarSource/sonarqube/blob/4bccde70aab57079a0c7b6055528f776fac315fe/sonar-scanner-engine/src/main/java/org/sonar/scanner/externalissue/ExternalIssueImporter.java#L120

If startColumn(= character in SwiftLint) is specified, it throws null pointer exception, since SwiftLint StyleViolation doesn't have endColumn, and endLine. So I skipped startColumn intentionally to avoid the exception.

That said, it's appreciated if you consider adding this feature to SwiftLint.

My code is junkpiano@eaff52c.
If you are OK with it, I can send PR.

[marcelofabri]

A PR would be welcome!

[marcelofabri]

Implemented on #2352.