apply some linters to R/

[MichaelChirico]

Part of #584

I applied several linters across R/ here:

• commas_linter
• trailing_blank_lines_linter
• spaces_left_parentheses_linter
• object_usage_linter
• function_left_parentheses_linter
• paren_brace_linter

I skipped equals_na_linter which only gives a spurious match that would be fixed by #546. Similarly there's a spurious instance of paren_brace_linter that applies to it's own source where "){" is present. We should move that linter to match on the parse tree as well.

[russHyde]

Hi. I moved paren_brace_linter over to the parse tree in #441 (which is now pretty out of date)