Add Open GL ES 2 dependency to AndroidManifest.xml by default

When using Qt Quick 2, your app will depend on OpenGLES2. This needs to be specified in the app's AndroidManifest.xml. Having smart logic here which detects the dependency and adds it automatically gets too messy, because you then need logic to check if it's been removed/added explicitly by the user, etc.

Instead, lets have a default which works. Lets make OpenGLES2 the default minimum version in the manifest, and then let people modify it if they know their app will support older versions.