Custom config.xml tags with App.appendToConfig

[fakenickels]

Re-open #5846, as requested by @zol :

As I also needed a solution for #5756, I attempted to implement it.
So now you're able to append custom tags to config.xml. Eg:

App.appendToConfig(`
  <universal-links>
    <host name="myhost.com"/>
  </universal-links>
`);

and config.xml will get:

<?xml version="1.0"?>
<widget id="com.example.ul" version="1.5.5" xmlns="http://www.w3.org/ns/widgets" xmlns:cdv="http://cordova.apache.org/ns/1.0">
  <name>UniversalLinks</name>
  <description>Another app</description>
  <author href="twitter.com/_gabrielrubens" email="grsabreu@gmail.com">Gabriel Rubens</author>

  <universal-links>
    <host name="myhost.com"/>
  </universal-links>
</widget>

Let me know how I can improve something!
Cheers

[zol]

Merged, thanks @grsabreu !

[fakenickels]

Awesome!