Better domain handling in createTask sender

[chmanie]

Currently the createTask sender requires a domainId to be set. We want to make it a little bit easier for people to use who don't want to concern themselves with domains. So it'd be good to set the default value of domainId to 1 (which is the root domain).

Also, when specifying a domainId which doesn't exist, we get a revert error. We should add some async validation so that it checks whether the domain exists before trying to create the task.

TODO:

• Make 1 the default domain
• Adjust the docs (also for the createTask sender) (@gichiba ?)
• Validate that the domain exists before trying to create a task

[gichiba]

I added language into the 'get started' doc for the above (into the PR #152), but I think the comments for senders should be changed in the PR that implements the actual code change, right?

[chmanie]

but I think the comments for senders should be changed in the PR that implements the actual code change, right?

Yes, I hope @JamesLefrere is going to take care of this