feat(analytics): add support for tracking control

Add support for the `trackers` property to the `player.options` in order to
store tracker instances. This makes it easier to access trackers directly from
the player. Use of this feature remains optional.

```javascript
// add custom tracker
const player = new Pillarbox('my-player', {
  trackers: {
    customTracker: new CustomTracker(player),
    anotherTracker: new AnotherTracker(player),
  }
})
```

Add the ability to disable trackers per playback session by introducing the
`disableTrackers` property provided directly to the `player.src`. As most trackers
take an instance of the player as a parameter. This will make it easier to access
the disableTrackers property to determine whether or not the tracker should be
disabled for the current playback session.

```javascript
// disable a tracker for the playback session
player.src({
  src : 'urn:xyz',
  type: 'srgssr/urn',
  disableTrackers : ['anotherTracker']
});

// disable all trackers for the playback session
player.src({
  src : 'urn:xyz',
  type: 'srgssr/urn',
  disableTrackers : true
})
```

Add support for SRG SSR-compliant media playback tracking.

- add `trackers` to Pillarbox default options
- add the `SRGAnalytics` class and unit tests
- add `PlayerEvents` that contains all `mediaElement` events
- srgssr middleware
  - add a function to handle SRG SSR analytics
  - update `composeSrcMediaData` to handle `disableTrackers`
  - move the construction of the main resources array into its own function
  - update unit tests

Refers to issue #32

package.json

@@ -1,7 +1,7 @@
 {
   "name": "@srgssr/pillarbox-web",
   "description": "Pillarbox is the modern SRG SSR player",
-  "version": "0.0.7",
+  "version": "0.6.9",
   "main": "dist/pillarbox.js",
   "targets": {
     "github-page": {