migrate saveToFile compatible with new renderer
RenderTexture saveToFile will return true
Merge branch 'develop' into develop_RenderTextureImprovement
Merge pull request #5654 from dabingnn/develop_RenderTextureImprovement

Develop render texture improvement
Re-add hellocpp, hellolua
Removes unused configuration for Xcode.
Adds lua-hello samples, it works on iOS / Mac .
Removes xcscheme for test project.
Renames cocos2d_samples to cocos2d_tests, what could i say?
Renames 'samples' folder to 'tests', ouch....
cpp-hello -> cpp-empty-test, lua-hello -> lua-empty-test, ouch....
lua-empty-test folder structure refactoring.
plist rename.
lua-empty-test, cpp-empty-test work for iOS/Mac
cpp-empty-test works ok for Android.
Remove .gitkeep in 'cpp-empty-test', Add proguard-project.txt.
All tests could run on Android.
[Android] Prefer to install tests to external storage device.
TestsDemo -> CppTests.
travis builds all tests projects for Android.