Consolidate and improve HERE T&C acceptance handling

We have code in the wizard and the security-privacy plugins for reviewing and accepting of the HERE T&C. We need to refactor this for better code reuse and language handling

This is some feedback I collected from @laney:

In reference to finding language specific html files containing the T&C:

<quote>
I think you should look at using the language plugin, because it understands this concept of default langauges and uses libicu's database to determine this. You'll probably have to extend it it a bit, but I think it's right to do that. Will Hua (attente on IRC) wrote this code, he's probably the guy to go to.
</quote>

and:

<quote>
I feel like some C++ here (using QFile::exists & friends) would be cleaner. This is essentially

  - can I find ll_cc.html?
  - no - can I find ll_default.html?
  - no - en_us please.

Then you'd avoid this iteration over the directory.
</quote>