Rename ubports to uuitk

Jonatan Hatakeyama Zeidlerrequested to merge
jonnius/convergence-components:uuitk into master

Renamed platform.ubports to platform.uuitk, because that is the toolkit's abbreviation and is short for Ubuntu UI Toolkit. The distro that uses the UUITK is Ubuntu Touch. Ubports is just the name of the community and foundation.

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