Add view properties animators

[natinusala]

We should be able to animate views / their properties. Animations can have multiple steps, animating multiple parts.

For example animate the scale from 0 to 1 in 10s then animate translationX for 25s while animating rotation for 10s, etc...

Animations could be defined programmatically but in XML files too if necessary. Since animations can have multiple steps / keyframes, it might be interesting to have a nice XML format to define it once and play it on multiple occasions. Or it might be overkill.

API is to be designed before starting working on this issue.