[bug#46012] Upgrade Nheko

[Nicolò Balzarotti]

Hi guix! Today nheko 0.8.0 was released.

This patch series upgrades it and its dependency, mtxclient.
I alsotook some time to unbundle all its dependencies (adding
cpp-httplib, blurhash, and single-applicaiton-qt5).

About this last dependency (single-applicaiton-qt5), I'm unsure on how
to name it.  Also, devs are suggested to include its source directly,
and by default builds a static library.  The main SingleApplication
class inherit from a Qt*Application class which is choosen at build
time, so the library to be useful in the target program must be built
with the correct flag (I'm using the one used by nheko by default).

Nheko builds and run fine.  It should support voice call now, but I
cannot test it (I get `[error] WebRTC: failed to start device monitor',
not sure if the problem is in my setup, in gstreamer or in my package).

0001-gnu-Add-cpp-httplib.patch
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0002-gnu-Add-blurhash.patch
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0003-gnu-mtxclient-Update-to-0.4.0.patch
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0004-gnu-Add-single-application-qt5.patch
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0005-gnu-nheko-Update-to-0.8.0.patch
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