Miss oriented custom actions while using ng2-smart-table with nebular themes

### Issue type

**I'm submitting a ...** (check one with "x")

* [x] bug report
* [ ] feature request
* [ ] question about the decisions made in the repository

### Issue description

**Current behavior:**

While using [custom actions](https://akveo.github.io/ng2-smart-table/#/examples/custom-editors-viewers) `ng2-smart-table` with the nebular theme.
the actions become missoriented.

**Expected behavior:**

Properly oriented actions, just as vanilla installation of `ng2-smart-table`

**Steps to reproduce:**

just add custom actions to settings of `ng2-smart-table`
```
settings = {
actions: {
add: false,
edit: false,
delete: false,
custom: [
{
name: 'customEdit',
title: 'CEdit ',
},
]
},
}
```

### Other information:

**npm, node, OS, Browser**
```

```

**Angular, Nebular, ng2-smart-table**