Add support for R language

[lo5]

Goal
Allow developing apps and dashboards in R; feature-parity with Python API.

Phases

• Initial qgen UI API scaffolding.
• Initial support for scripts (not apps), bundled as an R package that can be installed without CRAN (R CMD INSTALL?).
• Port 5-10 examples from Python to R.
• Use examples to refine API design.
• Ship support for scripts (dashboards only): Preview release of R client #612
• API improvements Improvements to R site/page API #773
• Plan support for apps.
• Implement R apps

[ashrith]

added a new issue. #433

[ashrith]

update: Testing for Plan support for apps. is going on.