Modified some constrains to works on iOS8 and iPhone6. closes #396

the constraints used on FeedbackViewController (with some smoothly managed exceptions) and EditTimeEntryViewController works better.
fixes #396
you´re right. You can´t not define the same constraint two times because it generates a conflict, you should remove it. But the best way to redefine it is using constants values ( not deleting and creating again). That´s what I read until now. 

In case of child objects, in my opinion, is better to define simple constraints only one time. In case of this button, if you delete it, next time (after remove-add) it takes a wrong height value. Like the billable switcher:

![screen shot 2014-12-19 at 11 48 17](https://cloud.githubusercontent.com/assets/1842773/5526739/2842e12e-89f7-11e4-9356-0afb2ea3b955.png)