Launching of an activated terminal

[DonJayamanne]

@brettcannon @qubitron @MikhailArkhipov
#383 we introduced the ability to pre-activate Python environment (e.g. Conda Environments) in the terminal opened when using the Python extension commands for:

• Launching REPL
• Running python code in terminal
• Running python file in terminal

None, of these commands allows a user to create a terminal with the python environment pre-activated.

Suggestion:

• Create a command Python: Create Termnial