Flatten routes 2 - channel list - channel edit modal and channel details modal

[MisRob]

Description

Another PR to flatten routes + related refactoring and cleanup.
I added another commit to shorten route paths (seems that there's no need to have channels two times in URL)

Collections will follow soon.

Steps to Test

Navigate to channel information and channel edit modals from channel lists and public catalog (these modals are also rendered when we navigate to them from channelEdit app though I haven't updated its routes in this regard yet, will follow in upcoming PRs). Check that back navigation works properly. Try to reload pages.

[codecov]

Codecov Report

Merging #2024 into develop will increase coverage by 0.01%.
The diff coverage is n/a.

@@ Coverage Diff @@## develop #2024 +/- ##
===========================================
+ Coverage 79.46% 79.47% +0.01% 
===========================================
Files 276 281 +5 Lines 13275 13318 +43 ===========================================
+ Hits 10549 10585 +36 - Misses 2726 2733 +7 

Impacted Files	Coverage Δ
contentcuration/search/viewsets/contentnode.py	58.51% <0.00%> (-3.56%)	⬇️
...ontentcuration/contentcuration/viewsets/channel.py	78.70% <0.00%> (-0.20%)	⬇️
contentcuration/contentcuration/utils/publish.py	77.03% <0.00%> (-0.08%)	⬇️
...uration/kolibri_content/migrations/0001_initial.py	100.00% <0.00%> (ø)
...entcuration/migrations/0112_merge_20200513_0049.py
...entcuration/migrations/0113_merge_20200513_2256.py
...ibri_content/migrations/0007_auto_20200613_0050.py	100.00% <0.00%> (ø)
...migrations/0115_index_contentnode_node_id_field.py	100.00% <0.00%> (ø)
...entcuration/migrations/0114_merge_20200806_1746.py	100.00% <0.00%> (ø)
...content/migrations/0008_channelmetadata_tagline.py	100.00% <0.00%> (ø)
... and 6 more

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[rtibbles]

A couple of questions.

[indirectlylit]

Minor note that as the number of constants and mappings between constants grows, maintenance can get a bit challenging.

Of course using constants is usually better than raw strings, but there are also some cases where this can be taken too far, and some other kind of abstraction is necessary.

As noted below, it's also important to clearly define what constants are used for, and use them only for that purpose. Otherwise we unintentionally couple things that have no need to be coupled.

[jayoshih]

Just one change on maintaining query params, but looks good otherwise!

[jayoshih]

Nice!!!