Replace all Lettuce specs by unittest+splinter

[rodrigomanhaes]

Lettuce approach adds one more level of indirection (specs in plain-English are translated into fragmented Python steps). Since we don't have a non-technical customer/user that takes advantage from our plain-English specs, replacing them by functional specs in unittest using a high-level API as Splinter will increase both readability and simplicity of our specifications.

[bernardobarreto]

is it really necessary at this point ? I think it would be much more hard work to change from lettuce than keep with it, because it's everything already done in the website, I mean, I don't think will come up something big that would be really easier test without lettuce.