feat: Permissions API

[mlynch]

This adds a new API called Permissions that lets a developer check if certain permissions have been granted yet before requesting them.

It largely follows the Permissions API in the browser.

Examples:

  async checkCamera() {
    const has = await Plugins.Permissions.query({ name: PermissionType.Camera });
  }

  async checkPhotos() {
    const has = await Plugins.Permissions.query({ name: PermissionType.Photos });
  }

  async checkGeo() {
    const has = await Plugins.Permissions.query({ name: PermissionType.Geolocation });
  }

  async checkPush() {
    const has = await Plugins.Permissions.query({ name: PermissionType.PushNotifications });
  }

Also couldn't help myself and fixed bug in the Geolocation API for Android where calling requestPermissions would cause the requestPermissions call to return over and over again, which really should only happen when the requestPermission called happened on watchPosition. I don't think this method is really used anyways

Also fixed a bug in Camera where it was creating the image picker on a background thread

[jcesarmobile]

Added two suggestions, will apply them

[jcesarmobile]

Added a few changes, but I'll make them

[jcesarmobile]

Suggested change

	import { IonicPage, NavController, NavParams, AlertController } from 'ionic-angular';
	import { IonicPage, NavController, NavParams } from 'ionic-angular';

remove unused AlertController

[jcesarmobile]

Suggested change

	private sanitizer: DomSanitizer,

[jcesarmobile]

Suggested change

	private alertCtrl: AlertController) {