Refactor|libshell: Separated history from CommandLineWidget

This refactoring allows the history buffer to be used with anything
that implements ITextEditor.
libdeng2|RuleRectangle: Using another RuleRectangle as the input
Refactor|Console: Moved the console lexicon collector to con_main

It was originally located in ShellUser.
libshell|AbstractLineEditor: Added a way to determine index's position on wrapped lines
Refactor|Games: Updated for DENG2_PIMPL, added game change audience
Client: Cleanup
Refactor|Games: ClientApp owns the Games collection

On the server, it still exists as a static variable in dd_main as
there is no ServerApp yet.
Client|LineEditWidget: Drawing an underline for the autocompletion
Client|Widgets: Added a console command widget

A specialized text editor that uses a history of previous entries,
automatically gets its lexicon from the console subsystem, and
executes console commands after they are entered.