Avoid shadowing variables:
* Rename variables to something better if possible
* If not, postfix shadowing arguments with _. Favour leaving member
variables without postfixes.
* Rename variables prefixed with _ to avoid library function collisions
* Avoid double underscore anywhere in names
* Make definition and declaration argument names match where seen
* Favour using class variable over argument variable, where equivalent
* Remove explicit this-> where equivalent
* Replace lines/messages with helper class to synchronize state between
IChatLog and ChatLog more easily
* selection indexes have been replaced with ChatLine::Ptrs, this is to
ensure consistency while the view slides around
* This has another benefit of removing all the code that has to
manually slide the selection boxes around
* Replaced all insertion/removal functions with single "insertAtIdx".
This helps ensure that mappings between ChatLogIdx and position within
the view are captured correctly as items in the view slide around
* workerTimeout replaced with more generic name "renderFinished" that is
used in synchronous and asynchronous paths
* Removed unused function ChatForm::insertChatMessage
* Re-implemented "Go to current date" with new ChatLog APIs
* Removed unused GenericChatForm::addSystemDateMessage. This is handled
by ChatLog now
* Resolves#6223
* Resolves#5878
* Resolves#5940
