Reset Vuex store on logout

[tobias-wiese]

Description

• Fixes Certificate is only shown after clicking of create, even if one exists #725

Reason for this PR

• The store was not resetted after logout, hence e.g. the certificate was not deleted

Changes in this PR

• add a default state
• add a mutation RESET_STATE that assign the default state to the store state
• commit the new mutation on logout

Type of change (remove all that don't apply)

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Manually tested all use cases this could alter

Test Configuration:

• OS: Windows

• Browser: Firefox

• Frontend: (remove all that don't apply)

  • Development build

• Backend: (remove all that don't apply)

  • No backend needed to test this
  • deployed development build

Checklist: (remove all that don't apply)

• I have performed a self-review of my own code
• My changes generate no new linting warnings or console warnings
• I have updated the CHANGELOG.md to include any changes made in this PR (add WIP to the top, if there is none already)