Bad timezone input validation

[vilhelmprytz]

Describe the bug
A partly valid timezone, e.g. Europe (which is included as a substring in timezones like Europe/Stockholm) will be accepted by the current input validation since it only checks if the user input string is somewhere to be found in the string with the list of all timezones. It does not check whether it's a "valid" timezone of its own.

To Reproduce
Steps to reproduce the behavior:

1. When the script asks to set a timezone, try an obviously invalid one to make sure that it actually doesn't allow you to input anything.
2. Enter something like Europe and notice that the script will accept it as valid, even though it isn't.

Expected behaviour
I expect the script to know the difference between valid timezones and substrings of valid timezones.

Screenshots

OS (please complete the following information):

• OS: all
• Installation: panel

Additional context
N/A

[vilhelmprytz]

Fixed by #143 (forgot to add in initial PR).