add fancy tech to allow calamares to reuse most of the ubiquity slideshow

Summary:

• new qml module which injects i18n into the engine so we may resolve translations from the existing gettext files. it also sets the correct domain and ensures the runtime language selection of calamares is forwarded into ki18n
• since the qtquick tech in cala feels like it's from 5 years ago we also force a proper background on the presentation now. meaning it no longer has this obnoxious white background associated with a qqmlview.
• new qml files loosely based on the existing one we have in calamares-settings
  • index.qml is similar to index.html in that it defines the general order of the show etc.
  • new UbiquitySlide.qml which extends cala's Slide with a generic as possible translation of the existing ubiquity htmls. to that end the Slide loads the related html file as xml and pops out the header string and the img uri. the string is then run through i18n to translate it accordingly
  • the header is now also using a Kirigami.Heading which is an easy way to get a header but also is vastly more useful than the originally suggested Text as it obeys colors and what not

all of this also requires changes to the packaging and calamares-settings
to actually get used

Test Plan:
in a testing VM it works as expected, since this is a
functionally large change affecting 3 repos this does also need testing
in the unstable edition tho

Reviewers: jriddell, bshah

Reviewed By: bshah

Differential Revision: https://phabricator.kde.org/D21250