✨ Adding new heading configuration

[vikripermana21]

Hi Kolkov!, i wanted to request a PR, this PR provide a feature that now headings can be customized. I hope u accept this PR. Thanks

[codecov]

Codecov Report

Patch coverage: 66.66% and project coverage change: +0.12 🎉

Comparison is base (40431f4) 20.66% compared to head (4179eef) 20.79%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #531      +/-   ##
==========================================
+ Coverage   20.66%   20.79%   +0.12%     
==========================================
  Files           8        8              
  Lines         479      481       +2     
  Branches      103      104       +1     
==========================================
+ Hits           99      100       +1     
  Misses        377      377              
- Partials        3        4       +1     

Impacted Files	Coverage Δ
projects/angular-editor/src/lib/config.ts	100.00% <ø> (ø)
...angular-editor/src/lib/angular-editor.component.ts	17.44% <50.00%> (+0.38%)	⬆️
...editor/src/lib/angular-editor-toolbar.component.ts	17.74% <100.00%> (ø)

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