Granular validation

[alcuadrado]

This PR closes #120

I tried adding a test for this at the end of the huge async.series call, but I can't get it run. It's ignored by tape. Any idea?

[alcuadrado]

@holgerd77 I updated this PR with the following changes:

1. Add a @deprecated tag in Blockchain's and BlockchainOptions' validate field.
2. Throw in the Blockchain constructor if both validate and validatePow/validateBlocks are used.
3. Always set Blockchain#validate as true and ignore its value.
4. Update the docs.

[holgerd77]

@alcuadrado Ahm, you still have to set the validate option if it is used, otherwise it is not a deprecation but a removal, or am I getting something wrong? 😛

[holgerd77]

Update: ah, I am getting something wrong, just seeing that you are directly assigning this to the specific valdation parameters. 😄

[alcuadrado]

There was a bug on how validate and the default values were handled. I fixed it and updated a test to be compatible with the changes introduced by this PR.

[holgerd77]

Looks good.