[cypress] beforeEach and before hooks need refactoring

```js
beforeEach('IDE', function(){
      cy.visit('/')
        .get('#theia-top-panel', {timeout: 60000})
        .should('be.visible')
        .get('.theia-preload').should('not.exist');
    })
```

is superflous to run before each test in `tree_spec,js` and `eval_panel.js` once should be enough, or does it do something meaningful that i m not getting?