fix(withWebComponent): Bind unknown events & cleanup

[MarcusNotheis]

BREAKING CHANGE:

Removed innerStyles prop in favour of css variables and UI5's addCustomCSS API

Fixes #181

[codecov-io]

Codecov Report

Merging #182 into master will increase coverage by 0.22%.
The diff coverage is 83.87%.

@@            Coverage Diff             @@
##           master     #182      +/-   ##
==========================================
+ Coverage   74.41%   74.64%   +0.22%     
==========================================
  Files         148      148              
  Lines        3389     3380       -9     
  Branches      594      592       -2     
==========================================
+ Hits         2522     2523       +1     
+ Misses        664      650      -14     
- Partials      203      207       +4

Impacted Files	Coverage Δ
packages/main/src/internal/withWebComponent.tsx	79.79% <83.87%> (+7.57%)	⬆️

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