Make Gradle wrapper executable on Linux and add IntelliJ .gitignore entries

.gitignore

@@ -11,15 +11,23 @@ gradle-app.setting
 
 # # Work around https://youtrack.jetbrains.com/issue/IDEA-116898
 # gradle/wrapper/gradle-wrapper.properties
-
 .classpath
 .project
 
----> Custom
+# IntelliJ
+
+.idea/
+out/
+*.iws
+*.ipr
+*.iml
+
+# ---> Custom
 !/libs/
 /.settings/
 /bin/
 /storage/
+
 #Generated Code
 /src/main/java/speiger/src/collections/booleans/*
 /src/main/java/speiger/src/collections/bytes/*