[WIP] Modifier with environment

[cornerman]

• add Environment to VMod
• fix
• more useful EventDispatcher
• Update sbt-scalajs, scalajs-compiler, ... to 1.15.0 (Update sbt-scalajs, scalajs-compiler, ... to 1.15.0 #755)
• fix typo in readme
• Update README.md
• Update colibri, colibri-jsdom, ... to 0.8.3 (Update colibri, colibri-jsdom, ... to 0.8.3 #758)
• update

[codecov]

Codecov Report

Attention: Patch coverage is 38.02083% with 119 lines in your changes missing coverage. Please review.

Project coverage is 55.67%. Comparing base (0863cbe) to head (cde4657).

Files	Patch %	Lines
outwatch/src/main/scala/outwatch/VMod.scala	41.42%	41 Missing ⚠️
outwatch/src/main/scala/outwatch/Render.scala	49.01%	26 Missing ⚠️
...watch/src/main/scala/outwatch/EmitterBuilder.scala	0.00%	21 Missing ⚠️
outwatch/src/main/scala/outwatch/AttrBuilder.scala	0.00%	13 Missing ⚠️
...ch/src/main/scala/outwatch/AccessEnvironment.scala	0.00%	7 Missing ⚠️
...in/scala/outwatch/helpers/ModifierBooleanOps.scala	0.00%	5 Missing ⚠️
...rc/main/scala/outwatch/helpers/NativeHelpers.scala	40.00%	3 Missing ⚠️
.../main/scala/outwatch/interpreter/SnabbdomOps.scala	0.00%	2 Missing ⚠️
...cala/outwatch/interpreter/ModifierToSnabbdom.scala	94.11%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #759      +/-   ##
==========================================
- Coverage   57.77%   55.67%   -2.10%     
==========================================
  Files          23       24       +1     
  Lines        1319     1383      +64     
  Branches       88       91       +3     
==========================================
+ Hits          762      770       +8     
- Misses        557      613      +56     

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