Merge rules EC505 and EC506 (Idleness: Keep Screen On (addFlags) - (setFlags))

[jhertout]

As said in this post by Ann, the rules EC505 and 506 are almost the same (their description is exactly the same). There is no real reason to have 2 rules, in the SonarQube implementation at least.

@olegoaer what do you think of this?