Add e2e tests

[Siegrift]

I'd like dashboard to be tested e2e as well...

Unfortunately, due to time pressure only simple tests were written, but I'd like to add more :)

However, I think our tests (for such a simple page) should be under 15 minutes and we shouldn't complicate things and focus on the most importants parts and user flows.

This includes

• Initial setup = Done in Setup cypress, write dashboard tests, fix go utility function #126
• Test dashboard flow = Done in Setup cypress, write dashboard tests, fix go utility function #126
• Implement code changes allowing switching accounts in e2e tests (read description of Setup cypress, write dashboard tests, fix go utility function #126)
• CI script #196
• Implement code for account switching and write tests using other accounts #157
• Test notifications (I think this can just be added to dashboard tests to save execution time)
• Test create proposal + form validation #181
• Test active proposals page (voting, navigation to invalid proposal page, after epoch length passed proposal should move to history page)
• Test history proposals page (execute, invalid proposal details page)
• Delegation + treasury
• Test mobile version (probably just a bit to save execution time)
• We have a lot of annoying styling special cases. I think it's worth adding some visual tests as well (https://docs.cypress.io/guides/tooling/visual-testing#Functional-vs-visual-testing)

[Siegrift]

We can use evm_snapshot to force a certain node state at each test. trufflesuite/ganache#37

[Siegrift]

Setup done in #126