Added Command class

Allows command to be executed.
Contains following methods:
executeProcessNoReturn:
- Executes any specified process with specified arg/s
- Doesn't return output (void)

executeProcessReturnLastLine:
- Executes any specified process with any specified arg/s
- Returns output's last line

executeProcessReturnAllOutput:
- Executes any specified process with any specified arg/s
- Returns entire output. (Recommended to be executed from external
thread/ other thread)