Source command is quiet by default

[flyingsilverfin]

What is the goal of this PR?

We make the source command not use the pretty-printer or wait for results unless specified with the --print-answers flag, which is optional.

What are the changes implemented in this PR?

• source now has an optional --print-answers
• when not printing answers, we execute all the queries in the query string as async queries, then wait for them all at the end
• define/undefine never are fully async, and ways do a get() on the query result.