Standardize naming delivery as shipment

[mad-anne]

Standardize naming delivery as shipment in UI, translation strings, comments and docstrings.

Closes #1361

Pull Request Checklist

1. Privileged views and APIs are guarded by proper permission checks.
2. All visible strings are translated with proper context.
3. All data-formatting is locale-aware (dates, numbers, and so on).
4. Database queries are optimized and the number of queries is constant.
5. The changes are tested.
6. The code is documented (docstrings, project documentation).
7. Python code quality checks pass: pycodestyle, pydocstyle, pylint.
8. JavaScript code quality checks pass: eslint.

[codecov-io]

Codecov Report

Merging #1410 into master will decrease coverage by <.01%.
The diff coverage is 33.33%.

@@            Coverage Diff            @@
##           master   #1410      +/-   ##
=========================================
- Coverage   82.91%   82.9%   -0.01%     
=========================================
  Files         128     128              
  Lines        5777    5775       -2     
  Branches      663     663              
=========================================
- Hits         4790    4788       -2     
+ Misses        831     830       -1     
- Partials      156     157       +1

Impacted Files	Coverage Δ
saleor/dashboard/order/forms.py	73.39% <ø> (ø)	⬆️
saleor/checkout/core.py	92.62% <ø> (ø)	⬆️
saleor/order/models.py	89.01% <ø> (+0.39%)	⬆️
saleor/dashboard/order/views.py	56.95% <33.33%> (ø)	⬆️
saleor/core/utils/__init__.py	76.59% <0%> (-1.07%)	⬇️
saleor/dashboard/customer/filters.py	100% <0%> (ø)	⬆️
saleor/dashboard/discount/filters.py	100% <0%> (ø)	⬆️
saleor/dashboard/category/filters.py	100% <0%> (ø)	⬆️
saleor/dashboard/product/filters.py	100% <0%> (ø)	⬆️
saleor/dashboard/group/filters.py	100% <0%> (ø)	⬆️
... and 6 more

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