Enable Dialog only for "Display for" set to "Single"

[ZitaNemeckova]

Closes #4142

Go to Automate -> Automation -> Custumization -> Buttons -> create/edit one -> set Dialog to something -> set Display for to List or Single and List-> save it

Before:

After:

Also sets Dialog to nil when List or Single and List is selected.

@miq-bot add_label bug, hammer/no

@romanblanco please review, thanks :)

[miq-bot]

Checked commit ZitaNemeckova@eeffd20 with ruby 2.3.3, rubocop 0.52.1, haml-lint 0.20.0, and yamllint 1.10.0
2 files checked, 1 offense detected

**

• 💣 💥 🔥 🚒 - Linter/Haml - Linter::Haml STDERR:

warning: parser/current is loading parser/ruby23, which recognizes
warning: 2.3.6-compliant syntax, but you are running 2.3.3.
warning: please see https://github.com/whitequark/parser#compatibility-with-ruby-mri.