Consistent language in cart or orders

[codejockie]

Resolves #2798

How to Test

1. Place an order
2. On the order completed page, under the "Your cart" section, you should now see "Items in order" instead of the former "Quantity Total" as shown in the image below:

3. Login as admin
4. Approve the order
5. On the Process Order Action View, you should now see "Items in order" instead of the former "Quantity Total" as shown below:

[machikoyasuda]

Thank you for using sentence case <3

[brent-hoover]

@rymorgan These changes seem fine but does somebody need to verify that we got all of them?

[rymorgan]

@zenweasel What's the best way of doing that? Can't we search the code to find where we are using this language (Quantity Total)? I can comb through the app and try to find all the places but that seems like I'll probably miss something.

[aaronjudd]

@rymorgan all labels are in i18n (en.json) files...

[rymorgan]

@codejockie did you double check the i18n (en.json) files for any more instances of 'Quantity total'? Please, do that and let me know all/any places that it's been changed so I can QA.

[codejockie]

@rymorgan okay, will do that and get back to you.

[codejockie]

@rymorgan I did a search for "Quantity Total" in this PR, and I came across none as I have replaced the instances where they once existed with the right words

[rymorgan]

@codejockie Great, sounds good. Should be good to go then.

[brent-hoover]

@codejockie You have a conflict you need to resolve, but otherwise good to go.

[codejockie]

@zenweasel conflict resolved.

[brent-hoover]

Ready to go.

[spencern]

After removing unused prop in f959388 this now passes eslint.