frontend: Fix some code inconsistencies

[tomtseng]

• Add missing requirement to requirements.txt
• Adjust some code inconsistencies
  • e.g., lambda_size is used as a keyword argument when no such keyword argument exists. Should be worker_size instead.
  • e.g., in examples/, giving GridSearch() a keyword argument of machines=[<tuple>] gives an error Invalid type for parameter Filters[0].Values[0], value: ('ec2-18-237-213-139.us-west-2.compute.amazonaws.com', '172.31.14.190'), type: <type 'tuple'>, valid types: <type 'basestring'>.

[tomtseng]

closing --- looks like a lot of older commits have been pushed to master, likely making the changes in this PR outdated.