Static command system and example scenes updates

- b21 compatible
- Introduced a more elegant way to define static commands with the use
of the CommandAttribute attribute
- Updated the example scenes and added a few new ones
- Added a flag to the console UI that determines whether or not to
immediately activate the console input when the console is opened
- Changed the font of the console output and console input to Roboto
Condensed and Roboto Regular respectively
- Changed the color scheme sightly again
- Renamed asset directory Source\Common\ to Source\Internal\
- Split the DefaultCommands class into HelpCommand, CommandsCommand and
QuitCommand classes and moved them to new asset directory
Source\Commands\
- Created new namespaces UnityConsole.Internal, UnityConsole.Examples
and UnityConsole.Test