Eslint rule for block curlies

[jacogr]

• Add curly rule to disallow single-line squashing with blocks, e.g. ifs
• Fix existing issues where we tripped the the new rule

Probably controversial, but has some good reasons and intent behind it -

• Codebase is consistent, no more stylistic/preference differences
• Codebase is fully clear as to intent and readable (leaving the squashing to Uglify)
• Coverage tools can properly report on statements hit, important as we expand in this area (single line if-then would show as covered even if just the condition is tested and then never was)
• Less chatter in PRs

[derhuerst]

Coverage tools can properly report on statements hit, important as we expand in this area (single line if-then would show as covered even if just the condition is tested and then never was)

Note that this is not true. Coverage tools that report on line hits will be fixed. Statement hits, which are more helpful, have worked before.

Still I support this because it makes the code more consistent and even line coverage is a useful metric.

[coveralls]

Coverage increased (+0.01%) to 86.503% when pulling 921b9d0 on js-eslint-consistency into 077069c on master.