talkatu/talkatu

45a3c612332c
Change the gtk requirement from 3 to 4 and remove gspell

Testing Done:
ran `meson --wipe` to verify no errors there, but there's a stack of compiler errors which is to be expected during this transition.

Reviewed at https://reviews.imfreedom.org/r/1230/
Talkatu is versioned in [mercurial](https://www.mercurial-scm.org/) and is
available on [keep.imfreedom.org](https://keep.imfreedom.org/talkatu/talkatu).
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