Dialer: Add a helpline phone book

* Expose the sensitive numbers to the user so they can easily call one
  of them
* Make sure to leave as few traces of access as possible:
  * Calling a number closes the helpline activity
  * Opening a link closes the helpline activity
  * Before opening a link, a warning about browser history appears

* This makes use of a changed xml-format, which now allows adding
  various things:
<item>
    <categories>violence|human trafficking</categories>
    <name>Some NGO or whatever</name>
    <number>1234</number>
    <anything>anything else</anything>
</item>

Includes:

Author: Luca Stefani <luca.stefani.ge1@gmail.com>
Date:   Sat Mar 13 17:37:29 2021 +0100

    Dialer: Move to SPN schema classes

    Change-Id: I2cd3706f64bf45a2a6dd53caa9d5da48cf93ea28

Author: Michael W <baddaemon87@gmail.com>
Date:   Sat May 22 16:38:57 2021 +0200

    Dialer: Helplines: Add Bullying and Immigration categories

    Change-Id: I7969fd0dd610a4f041f55ce04e6ede5c66005dee

Author: Luca Stefani <luca.stefani.ge1@gmail.com>
Date:   Fri Mar 26 14:20:33 2021 +0100

    Dialer: Helplines: Use a webview dialog

    * Instead of relying on one browser we can actually display a webview
      ourselves
    * Set various headers to clear cache and to not track
    * Displays a progressbar and loading text while the page loads

Co-authored-by: Michael W <baddaemon87@gmail.com>
    Change-Id: Ibad2832c0cb6bcef79b5f348c40ca76c2516b295

Author: Michael W <baddaemon87@gmail.com>
Date:   Fri May 28 19:08:24 2021 +0200

    Dialer: Helplines: Fix a few casing issues

    Change-Id: I31c2423aee5310ae08c9295971fbe7aced1f8f9b

Change-Id: I952bf10ee9516b83e595d8a19450696b303393b6