Remove apollo-plugin Gradle plugin

Replaces the old Gradle plugin with plain Gradle buildscripts.  Also cleans-up
the current Gradle extensions and re-adds detekt, along with JUnit 5 support to
all modules.

game/plugin/areas/build.gradle

@@ -1,6 +1,12 @@
-plugin {
-    name = "Area listeners"
-    description = "Enables plugins to listen on mobs entering, moving inside of, or leaving a rectangular area."
-    authors = ["Major"]
-    dependencies = ["api"]
-}
+apply plugin: 'kotlin'
+
+description = 'Enables plugins to listen on mobs entering, moving inside of, or leaving a rectangular area.'
+
+dependencies {
+    implementation project(':game')
+    implementation project(':cache')
+    implementation project(':net')
+    implementation project(':util')
+    implementation project(':game:plugin:api')
+    testImplementation project(':game:plugin-testing')
+}