Target only the main repo branches by default

[sylvain-combe-sonarsource]

In most cases, there is no need to evaluate the LoC counts of every branch of every project as the variations should be very minor, and well within the error margin for this script. Let's make the simpler and faster behavior the default one.

[sylvain-combe-sonarsource]

https://github.com/SonarSource/sonar-loc-count/issues/23 should be implemented first

[brian-cipollone-sonarsource]

Note that this was the original behavior. I agree that this is overkill for the purpose of these scripts.