Ability to customise card set

[gmannGlasswall]

We've started playing with the estimate feature and are finding that the available card sets don't really work for us. We can probably adapt to the numbers but it would be nice to add our own.

Additionally we do offline estimation and have a wide variety of skillsets and some people are unable to estimate on some tasks or stories as they don't have the required skills to make a sensible estimate. We'd like to be able to add a card to indicate that someone has looked at an item but doesn't have the necessary knowledge to estimate.