Add and apply Style/InvertibleUnlessCondition rule

This rule was added in rubocop 1.44.0. It's useful to avoid accidental
`unless !condition` clauses.

Note we aren't replacing `unless zero?` with `if nonzero?` because we
never use `nonzero?`; using it sounds like `if !zero?`.

Replacing `unless any?` with `if none?` is only consistent if we also replace
`unless present?` with `if blank?`, so we're also adding this case. For
consistency, we're also replacing `unless blank?` with `if present?`.

We're also simplifying code dealing with `> 0` conditions in order to
make the code (hopefully) easier to understand.

Also for consistency, we're enabling the `Style/InverseMethods` rule,
which follows a similar idea.

app/controllers/officing/base_controller.rb

@@ -30,7 +30,7 @@ class Officing::BaseController < ApplicationController
     end
 
     def verify_booth
-      return unless current_booth.blank?
+      return if current_booth.present?
 
       booths = current_user.poll_officer.todays_booths
       case booths.count