Rename Tails Installer as Tails Cloner

Now that we are distributing USB images:

Tails Installer only exists in Tails (it used to be in Debian and Ubuntu as well)
Tails Installer is no longer the preferred way of installing Tails on USB stick (it used to be the case back in the days)

I think that it’s weird to call it “Tails Installer”. What remains from its use cases is to clone a Tails, either for installing or for upgrading and I think that we should rename it accordingly.

Using the “Use a downloaded Tails ISO image” option of Tails Installer it’s still possible to install Tails without cloning, but as analyzed on #16906, I guess that this feature is not used very frequently.

I also expect that renaming to “Tails Cloner” will make it much easier for users to discover that it is possible to do such thing as cloning Tails; keeping in mind that now that we distribute USB images, people never use Tails Installer to install it from scratch.

So this change is not only aesthetic :)

Related issues

Related to #14544
Related to #7049
Related to #16721 (closed)

Original created by @sajolida on 16907 (Redmine)

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