Adding functionality to select tab page according to the index

[fabio-nogueira-almeida]

I created this functionality because sometimes we need to call a tab page after some user action.

[fabio-nogueira-almeida]

This pull request solve two issues: #13 and #15

1 - Adding functionality for select tab. Now we can select some tab after user action 2 - Fix lost index when the device is rotated.

I tried to write code without erase or change the code already inside the project. So, in the future we can refactor the code for a better code.

[guilhermearaujo]

Nice job! Sorry for taking so long, I'll try to update the pod specs in the next hours.