Improve Promotions UX

[MatthewKennedy]

• Set layout to use full width for all fields in mobile.
• Set Select2 multiple choice fields to have same border radius, and height as other input fields, even when empty.
• Make panels more consistent looking for rules and actions.
• RULE: 'Order total meets these criteria' now makes more sense on mobile size screens.
• Add date/time picker to promo start from / expires at.

[squash-labs]

Manage this branch in Squash

Test this branch here: https://matthewkennedyfix-promos-54axi.squash.io

[damianlegawiec]

The Date picker in promotions was type datetime_field, everywhere else it is type text_field, so I changed it to match the others, what is the best field to use?

This change was made via #9450 to enable setting also a time of start/end of promotion as promotions are very time-sensitive :)

[MatthewKennedy]

@damianlegawiec Shall I update that date picker to a date/time picker and change the field type back?

[damianlegawiec]

@MatthewKennedy that would be awesome, please do! :)

[MatthewKennedy]

@damianlegawiec - I’ll do that today.

[MatthewKennedy]

@damianlegawiec I feel that the javascript for the flatpickr.js date and date/time pickers could be written better.

I'll target that in a dedicated PR.