Allow Signature Spoofing

[okias]

Signature Spoofing is important feature for being able use open-source microG (alternative to proprietary openGAPPS).

openGAPPS suite is signed by Google, it's by default Android (Google) rules is impossible to replace it.
Signature Spoofing allows microG to respresent itself as openGAPPS which leads to correct behaviour, when GAPPS API are used by application.

There are multiple approaches, but I'd recommend use the preferred one by microG developers (since, microG is main user of this feature).

microG wiki
XDA developers summary
Patches from microG developers for each Android version.

By allowing Signature Spoofing, you're not only allowing users to have more freedom over their emulator (since GAPPS are required for most of Android application) without additional troubles with patching their emulator, but also ease process of installing microG for newbies, which is important for reaching bigger microG userbase with open software.

Thank you for your work on ANBOX 👍

See also: #27