Present user with dialog when TLS cert warnings detected: Bug #713247
When a TLS certificate warning is detected, the user will now be presented with a warning dialog presenting them with three options: Trust This Server, Always Trust This Server, and Don't Trust This Server (the default). The user must select one of the first two buttons for Geary to continue connecting to the server, otherwise it will close the Account object for the duration of the application session. This patch introduces a dependency on gcr-3, which is used to pin TLS certificates (i.e. persist the user's choice of ignoring the TLS warnings).