More layoutlib testing infra fixes

- Remove ModuleClassLoader as it can be replaced with a URLClassLoader
  for now.
- Move CustomCalendar and CustomDate to a separate package that can be
  used both by the Bridge tests and the actual test app.
- Move empty.xml out of the test app so it compiles.
- Update test app to use the latest build tools and SDK (some attributes
  being used by the app weren't supported in API 21).
- Update gitignore to remove the new out directory.

Test: Update to existing tests
Change-Id: Ieb7324d5ae559f9c581771c57f2127cd83909015
diff --git a/bridge/bridge.iml b/bridge/bridge.iml
index 57d08cb..fbaed52 100644
--- a/bridge/bridge.iml
+++ b/bridge/bridge.iml
@@ -7,6 +7,7 @@
       <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/tests/res" type="java-test-resource" />
       <sourceFolder url="file://$MODULE_DIR$/tests/src" isTestSource="true" />
+      <sourceFolder url="file://$MODULE_DIR$/tests/res/testApp/MyApplication/src/main/myapplication.widgets" isTestSource="true" />
       <excludeFolder url="file://$MODULE_DIR$/.settings" />
       <excludeFolder url="file://$MODULE_DIR$/bin" />
       <excludeFolder url="file://$MODULE_DIR$/tests/res/testApp/MyApplication/.gradle" />