Allow source sets to be included/ignored

[ouchadam]

As a user of this plugin I would like to run evaluateViolations but only on my main source set (no unit/instrumentation tests or flavours)

[eduardb]

I would add that for Android modules, have a way to include/exclude variants.

[mr-archano]

Followed up this with @ouchadam in slack: sourcesets can be already ignored via the exclude filters. The problem is related to the fact evaluateViolations is a unique task, which depends on all the static analysis task. It's not possible at the moment to specify to check a specific sourceset/variant only (eg: evaluateViolationsMain or evaluateViolationsDebug).

I'm reluctant to add this feature because I feel will disrupt the evaluation of the thresholds: are those gonna be global values? per variant values? what when we want to include more than one variant then?

@ouchadam @eduardb I'm happy to take a look at the issue that you're facing at the moment and try to understand further.

[mr-archano]

Fixed in #28