Added a simple command history for the IDE's console

Thought I'd go ahead and submit a pull request for this, in case you think it's useful enough to put in the main project, Ivan. If there's any problems, let me know.

So basically you just use the up and down arrow keys when the console input is focused to scroll through a recent history of issued commands. I arbitrarily set the max size of the history to 15 entries. When a new entry is added via command execution, and the max history size is exceeded, the oldest command is pushed out. (If this is used, maybe max size can be configured as a global Polycode setting when that is implemented?)