Make example in inst/example consistent with other package examples

[ilyaZar]

Possible inconsistency or redundant example

This may really be nothing, or can be deleted altogether, but I do not quite see the point of inst/example/Untitled.R (probably some forgotten artefact @ColinFay ), so if it's meant to stay, I just cleaned up that file:

• change name to inst/example/examples.R
• rename plop,.... trigger names to airquality, iris etc.
• add comments
• change order of assignment/computations inside reactives:
  • computations happen in the beginning
  • triggers are called at the end of each reactive (observeEvent/ on, respectively) -> makes usage of triggers consistent with other package examples

[ColinFay]

Good catch :) That's indeed a forgotten artifact.

Thanks !