Integrate vcard4android as an android library (bitfireAT/davx5#300)

* Migrated to external dependency for vcard4android

Signed-off-by: Arnau Mora <arnyminerz@proton.me>

* Removed vcard4android submodule

* Update vcard4android version, remove from settings.gradle

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Signed-off-by: Arnau Mora <arnyminerz@proton.me>
Co-authored-by: Ricki Hirner <hirner@bitfire.at>