Android NDK version specifications are inconsistent in settings files #8

Entries in .cproject, .project, .settings (inside GameEngine-android) are not consistent.

We should at least unify them to Android NDK r9. And if possible, we could find some ways to set them depend on users' environments(Mac/Linux/Windows). Or, we should prepare a room for those settings in our documentation.

pointed out by @ynakanishi & @zaki50