Translation updates

[benjaoming]

Summary

• Documentation
• Make target msgids for generating translation sources
• Do not hide "IGNORE_PATTERNS" in a Python file, moved them to the Makefile
• Adds the sources to the repo so we can track them moving forwards

TODO

If not all TODOs are marked, this PR is considered WIP (work in progress)

• Has documentation been written/updated?
• Have you written release notes for the upcoming release?

Reviewer guidance

Let me know if I missed something in the way we generate msgids!

Issues addressed

#5477

[codecov]

Codecov Report

Merging #5485 into 0.17.x will increase coverage by 0.34%.
The diff coverage is 93.75%.

@@            Coverage Diff             @@
##           0.17.x    #5485      +/-   ##
==========================================
+ Coverage   61.98%   62.33%   +0.34%     
==========================================
  Files         118      118              
  Lines        6582     6582              
==========================================
+ Hits         4080     4103      +23     
+ Misses       2502     2479      -23

Impacted Files	Coverage Δ
kalite/i18n/management/commands/makemessages.py	95.83% <93.75%> (+95.83%)	⬆️

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[radinamatic]

OK, we are not done with this, yet...

This is what the Coach tools looks like after updating to the latest content pack in Spanish

Strings still in English:

All selected inside the topic selector and the Submit button.
Search string inside the search field.
N/A value for the summary of total hours on content compared to total hours connected.
Key string for the tabular report colors.

Disregard the strings with orange overlay, as that is a different issue (already reported), which we have to correct nevertheless... 😉

@mrpau-eduard @benjaoming I believe we should correct this too, before releasing 0.17.2.

[benjaoming]

@radinamatic

Some of these examples are unfortunately from JS libraries that aren't translated:

• All selected is from node_modules/bootstrap-multiselect/dist/js/bootstrap-multiselect.js
• Search is from node_modules/bootstrap-multiselect/dist/js/bootstrap-multiselect.js

I've opened #5496 for the two others.