Problem with disable attribute behavior on nb-action

### Issue type

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

* [x] bug report
* [ ] feature request

### Issue description

**Current behavior:**
Using the disabled attribute on nb-action tag doesn't stop the click event from executing.

**Expected behavior:**
Using the disabled attribute on the nb-action tag should stop the click event.

**Steps to reproduce:**
1. Set up Nebular in the Angular app
2. Create a new component with the following template:
```

```
3. With the following component logic:
```
...
export class NewComponent {
handleClick(): void {
console.log('Clicked!');
}
}
```

**Related code:**
https://stackblitz.com/edit/nebular-action-disable?file=src/app/app.component.html

### Other information:

**npm, node, OS, Browser**
```
Node: v11.9.0
NPM: v6.5.0
Angular CLI: 7.3.9
OS: Windows
Browser: Chrome
```

**Angular, Nebular**
```
"@nebular/date-fns": "3.4.0",
"@nebular/moment": "3.4.0",
"@nebular/theme": "3.4.0",
"nebular-icons": "^1.1.0",

"@angular/animations": "^7.2.7",
"@angular/cdk": "^7.3.3",
"@angular/common": "~7.2.7",
"@angular/compiler": "~7.2.7",
"@angular/core": "~7.2.7",
```