libhandy: adopt, various improvements

[paper42]

• enable tests
• install demo to libhandy-demo
• fix license
• combine vala and gir build options

General

• This is a new package and it conforms to the quality requirements

Have the results of the proposed changes been tested?

• I use the packages affected by the proposed changes on a regular basis and confirm this PR works for me
• I generally don't use the affected packages but briefly tested this PR

[paper42]

one test fails, but it works on my system:

The output from the failed tests:

19/22 test-swipe-group         FAIL           0.23s (killed by signal 5 SIGTRAP)

--- command ---
17:34:11 G_TEST_SRCDIR='/builddir/libhandy-v0.0.13/tests' PYTHONDONTWRITEBYTECODE='yes' GSETTINGS_BACKEND='memory' G_DEBUG='gc-friendly,fatal-warnings' MALLOC_CHECK_='2' G_TEST_BUILDDIR='/builddir/libhandy-v0.0.13/build/tests' /builddir/libhandy-v0.0.13/build/tests/test-swipe-group
--- stdout ---
# random seed: R02S05af253c32dbaf8a702833509942dece
--- stderr ---
Unable to init server: Could not connect: Connection refused

(/builddir/libhandy-v0.0.13/build/tests/test-swipe-group:4586): Gtk-WARNING **: 17:34:11.398: cannot open display: :99
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