Set default theme by default

[gustaphe]

Solves #4398

I'm not entirely sure why #4398 happens, I can't track down any of the awkward settings to any setting in Plots, PlotsThemes or anywhere else I could think of. But if you supply a theme it doesn't happen, and giving :default if no other theme is supplied should be pretty uncontroversial.

[t-bltg]

LGTM, pending CI.

[codecov]

Codecov Report

Base: 80.78% // Head: 80.40% // Decreases project coverage by -0.37% ⚠️

Coverage data is based on head (18310fb) compared to base (2823d49).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4420      +/-   ##
==========================================
- Coverage   80.78%   80.40%   -0.38%     
==========================================
  Files          30       30              
  Lines        7448     7171     -277     
==========================================
- Hits         6017     5766     -251     
+ Misses       1431     1405      -26     

Impacted Files	Coverage Δ
src/init.jl	100.00% <100.00%> (ø)
src/consts.jl	66.66% <0.00%> (-8.34%)	⬇️
src/axes.jl	84.06% <0.00%> (-2.07%)	⬇️
src/backends/unicodeplots.jl	86.52% <0.00%> (-1.04%)	⬇️
src/backends/pgfplotsx.jl	75.45% <0.00%> (-0.82%)	⬇️
src/backends/hdf5.jl	82.30% <0.00%> (-0.72%)	⬇️
src/backends/gr.jl	88.27% <0.00%> (-0.61%)	⬇️
src/backends/gaston.jl	82.00% <0.00%> (-0.58%)	⬇️
src/examples.jl	91.04% <0.00%> (-0.39%)	⬇️
src/pipeline.jl	95.90% <0.00%> (-0.23%)	⬇️
... and 12 more

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[gustaphe]

I'm taking the liberty of ignoring codecov - this simply lowers coverage by decreasing the number of loc.

[t-bltg]

I'm taking the liberty of ignoring codecov

We all do that ;)

[gustaphe]

Okay, there's a double commit now. Next time I'll get it right ...

[t-bltg]

Regarding the Plots versions increment, we usually wait a few days (typically a week) between patches unless something urgent (precompilation, dependencies, affecting lots of users) requires it, and avoid flooding the registry with new versions for a single Plots commit.

There was a lot of versions in 1.34.x in a small time window because of nasty GR issues induced by the transition from GR@0.68 to GR@0.69 were affecting lots of user on windows and macOS.

I've tagged 1.35.1 today, because GR@0.69.3 would potentially fix #4415, and this affects potentially hundreds if not thousands of macOS users.

So 1.35.2 could have waited a few days I guess (and IMO !) ...
Just a word on common practices here, nothing serious ;)

Cc @BeastyBlacksmith.

[gustaphe]

Mea culpa, I'll be less trigger happy in the future.