Implement GnuPG pinentry program instead of Gnome Keyring GnuPG agent

by Watson Yuuma Sato for GNOME

GNOME Keyring GnuPG Agent is currently incompatible with newer versions of GnuPG, it is not capable of providing all the functionality expected by GnuPG and ends up degrading some functionalities. This project is about making them compatible, so that GNOME Keyring can manage GnuPG passphrases again. The proposal is to implement a pinentry, a dialog that allow GnuPG to prompt for passphrases, that can search and store passphrases in keyrings, and prompt for it if not found.