add all modules, better gradle setup, and elixir for server

plt-server/build.gradle.kts

@@ -0,0 +1,10 @@
+tasks.register("compileEx", Exec::class) {
+    group = "elixir"
+    workingDir(project.layout.projectDirectory)
+    commandLine("mix", "compile") //TODO
+}
+tasks.register("testEx", Exec::class) {
+    group = "elixir"
+    workingDir(project.layout.projectDirectory)
+    commandLine("mix", "test")
+}