Trigger error when torque tile request fails

[xavijam]

Related ticket: https://github.com/CartoDB/cartodb.js/issues/1717

When the user reaches its limits, torque tiles could be affected, so the idea is to warn CARTO.js about that problem and then it should trigger that error accordingly.

Caveats

• We need to research if we could "render"/draw an error tile in the torque canvas.

[rubenmoya]

Close via #288

[xavijam]

Pero que buenos sois.