infrastructure: function to capture traceback with full-path filenames
show (currently useless) traceback button and wrapper around errors
Merge remote-tracking branch 'origin/master' into feature/error-management
simple display of traceback for errors via client event
register error handler on session start; factor error UI to UIBinders
match console errors to errors emitted from custom error handler
clickable source links in error tracebacks
add error management menu & commands
apply styling to traceback button
implement break-always strategy and command
implement "break in my code"; refactor some common R code
add error popup menu to console window frame (rough)
make window frame right-widgets generic
some infrastructure to support reporting changes in the error handler
fix promise evaluation display when promise SEXP is simultaneously eval'ed and assigned
show currently selected error handler in the client
add 'ignore errors' command and implementation
make callstack look more rational in Break Always mode
improve callstack display for Break in My Code
show line numbers in error traceback