introactivity: allow to override onCreate again

[amartinz]

• remove final from onCreate to allow overriding
• as the library depends on calling onCreate, add a CallSuper annotation to tell the library user that super.onCreate has to be called

Change-Id: Iee55651b080c05c6d655666a3c449d4ea5691b51 Signed-off-by: Alexander Martinz [email protected]

[MizzleDK]

Thanks for all your pull requests! I'm sorry I haven't seen them before now. Will take a look at them within the next few days.