Add happypack for babel-loader

What does this MR do?

Adds happypack for babel-loader parallel transform (default use of 3 threads) -cough forks cough-.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

# without happypack
26219ms = 26,219 ms
27737ms = 27,737 ms
25884ms = 25,884 ms
_without = average to minutes = 0 min 27 s

# with happypack
19590ms = 19,590 ms
18612ms = 18,612 ms
19446ms = 19,446 ms
_with = average to minutes = 0 min 19 s

# savings
_with as a % off _without = 27.8 % 

without

with

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?