No more warnings in "shiny" exception template if headers were already sent
Not raise any errors in "shiny" exception template if $context or $container are not defined
Always open the trace in "shiny" exception template if only a single stack entry is given
add CHANGELOG for #1478
Merge ac2ca4f...865bd9a (from pr-1478)

closes #1478

* exception-template:
  865bd9a add CHANGELOG for #1478
  cc0fc67 Always open the trace in "shiny" exception template if only a single stack entry is given
  f854f88 Not raise any errors in "shiny" exception template if $context or $container are not defined
  ac2ca4f No more warnings in "shiny" exception template if headers were already sent