Added horizontal course plan widget

.devcontainer/Dockerfile

.devcontainer/devcontainer.json

.gitignore

build.sbt

deployscripts/compiled.js

index-fastopt.html

index.html

project/build.properties

project/plugins.sbt

src/main/scala/courses/Course.scala

src/main/scala/courses/HPlanPrereqWidget.scala

src/main/scala/courses/PlanPrereqWidget.scala

src/main/scala/courses/Unit.scala

target/scala-3.0.0/acsmappings2022-fastopt.js

target/scala-3.0.0/acsmappings2022-opt.js