added: getExclusiveCommandOptionText

build upon previous pull request #61  #8

e.g. code 
```
commandOptionList = ['--available', '--installed']
userProgramList, userOptionList = subuserlib.utils.getUserCommandLine(sys.argv[1:], commandOptionList)

#Check exclusive commands
if '--available' in userOptionList and '--installed' in userOptionList:
  print("\nEXCLUSIVE-OPTION-ERROR: you can not use these options together:")
  exclusiveCommandOption = ["--available", "--installed"]
  print(subuserlib.utils.getExclusiveCommandOptionText(exclusiveCommandOption, addNewLine=True, indentSpaces=3))
  sys.exit()

```

output
```
workerm@notebook:~$ subuser print-dependency-matrix --installed --available

EXCLUSIVE-OPTION-ERROR: you can not use these options together:
   --available
   --installed

workerm@notebook:~$ 
```