This also fixes an issue with the use of the Iconics library where it was
initialized twice. I also removed the dependency to [AndroidX Preference
eXtended](https://github.com/takisoft/preferencex-android), as there don't seem
to be any issues with using the vanilla AndroidX preference library anymore.
This patch introduces the new ``UUIDMap`` type, reducing code duplication and
making UUID lookups faster. We currently already use UUIDs as the identifier for
the ``DatabaseEntry`` and ``Slot`` types, but the way lookups by UUID work are
kind of ugly, as we simply iterate over the list until we find a match. As we're
probably going to have more types like this soon (groups and icons, for
example), I figured it'd be good to abstract this away into a separate type and
make it a map instead of a list.
The only thing that has gotten slower is the ``swap`` method. The internal
``LinkedHashMap`` retains insertion order with a linked list, but does not know
about the position of the values, so we basically have to copy the entire map to
simply swap two values. I don't think it's too big of a deal, because swap
operations still take less than a millisecond even with large vaults, but
suggestions for improving this are welcome.
I had to update gradle and JUnit to be able to use the new ``assertThrows``
assertion method, so this patch includes that as well.
