Add time zone to events table

[katjuell]

Description

Adds timezone column to events table.

Test process

Time zone column should be present, and should look correct.

Requirements to merge

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [ ] I have commented my code in hard-to-understand areas
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes