Fix track ordering of hierarchical track selector to more closely match the config.json

[cmdcolin]

The current code for the ordering of tracks in the hierarchical track selector has a line that uses splice to make sure that "tracks are grouped together above category nodes".

If this is not done (e.g. if splice is changed to a push), then tracks can appear after category nodes which is a bit odd

Here are some screenshots showing the different configurations

With push instead of splice:

Current main:

This branch:

[cmdcolin]

Addresses some concerns from #26 but does not technically fix that issue, since that includes collapse by default and alt sorts

[cmdcolin]

code for creating the test_order config.json

jbrowse add-assembly volvox/volvox.fa --load copy --out test_order
for i in {1..5}; do echo $i; jbrowse add-track volvox/volvox-sorted.bam --load inPlace --out test_order --trackId "$i toplevel"; done;
for i in {1..5}; do echo $i; jbrowse add-track volvox/volvox-sorted.bam --load inPlace --out test_order --trackId "$i cat1" --category cat1; done;
for i in {1..5}; do echo $i; jbrowse add-track volvox/volvox-sorted.bam --load inPlace --out test_order --trackId "$i cat1 cat2" --category cat1,cat2; done;
for i in {1..5}; do echo $i; jbrowse add-track volvox/volvox-sorted.bam --load inPlace --out test_order --trackId "$i cat3" --category cat3; done;
for i in {1..5}; do echo $i; jbrowse add-track volvox/volvox-sorted.bam --load inPlace --out test_order --trackId "$i cat3 cat4" --category cat3,cat4; done;
for i in {6..10}; do echo $i; jbrowse add-track volvox/volvox-sorted.bam --load inPlace --out test_order --trackId "$i toplevel"; done;
for i in {6..10}; do echo $i; jbrowse add-track volvox/volvox-sorted.bam --load inPlace --out test_order --trackId "$i cat1" --category cat1; done;
for i in {6..10}; do echo $i; jbrowse add-track volvox/volvox-sorted.bam --load inPlace --out test_order --trackId "$i cat1 cat2" --category cat1,cat2; done;

[codecov]

Codecov Report

Merging #3808 (cb9b05a) into main (03c381d) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #3808   +/-   ##
=======================================
  Coverage   64.46%   64.46%           
=======================================
  Files         990      990           
  Lines       29580    29581    +1     
  Branches     7096     7097    +1     
=======================================
+ Hits        19068    19070    +2     
+ Misses      10347    10346    -1     
  Partials      165      165           

Impacted Files	Coverage Δ
...TrackSelectorWidget/components/tree/TrackLabel.tsx	80.00% <100.00%> (ø)
...ement/src/HierarchicalTrackSelectorWidget/model.ts	84.34% <100.00%> (+0.13%)	⬆️

... and 5 files with indirect coverage changes

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