No bug - Make project-wide default language level be Java 1.7 in IntelliJ. r=me

DONTBUILD NPOTB

Straight from http://stackoverflow.com/a/24751182 and the linked
IntelliJ tickets.

--HG--
extra : commitid : AcbSF0042KW
extra : rebase_source : f67e9eecfdf3f452e4fd55901f8eb42b0f3ed22c

mobile/android/gradle/build.gradle

@@ -73,3 +73,11 @@ afterEvaluate {
         }
     }
 }
+
+apply plugin: 'idea'
+
+idea {
+    project {
+        languageLevel = '1.7'
+    }
+}