Error indicator

[ptitFicus]

Here is what I did for #49
I tried to keep the behaviour of error as close a possible from the current print behaviour.
There is a few things I'm not 100% satisfied with :

• There is huge logic duplication between ErrorCross and TailSpin (and their tests) : we may want to factorize some code
• The isInState function in core.jsx is not super clear

Any suggestion / improvement / fix appreciated :)

[fabienjuif]

Great work, once again ;)
My first comment, I read it fast :

• I think the isInState name is not great indeed, at first I was expecting that you will use react state
• I agree with you about TailSpin + ErrorCross code factoring
• I think a test is missing : there is error prop test ?

1. The component is printed with default loader parameters
2. The error prop is set to true
3. The Cross should be printed

[fabienjuif]

@ptitFicus I close the PR since:

1. It is old now
2. There is a lot of conflicts

Feel free to reopen, and sorry about that :(