[mcp-account-manager] Implement get_additional_info to provide display names

This provides both the account and provider display name to clients.
[mcp-account-manager] Use account name for DisplayName again

The account name can change, but provider name cannot. DisplayName is
able to signal changes, while storage info is not.
[telepathy-sasl-signon] Use booster for launching

libsailfishkeyprovider is a privileged resource, so we need to launch
via the booster to gain privileges. Some careful systemd work related to
mission-control-5 will be done to make sure that booster-generic is
alwyas available when necessary.
Merge pull request #14 from special/use-booster

[telepathy-sasl-signon] Use booster for launching
Merge pull request #13 from special/master

Revert "Revert "[mcp-account-manager] Delay creating accounts until enabled for the first time"
[telepathy-sasl-signon] Don't set CredentialsNeedUpdate on global service

Instead, set it on the service which we're using for the account.
Also, print a debug line to the log when raising the flag.
[telepathy-sasl-signon] Only set CredentialsNeedUpdate flag when appropriate

Previously, the CredentialsNeedUpdate flag would be set in a variety
of situations, including when a generic OperationFailed error occurred.
This commit ensures that it is only set for an account when a
UserInteraction error occurs (that is, the account credentials are
valid but need to be refreshed manually by the user).
Merge pull request #15 from chriadam/cnufixes

Fix some issues with CredentialsNeedUpdate handling
Merge pull request #10 from special/additional_info

[mcp-account-manager] Implement get_additional_info to provide display names
[telepathy-sasl-signon] Only trigger CredentialsNeedUpdate for specific SASL errors

Unfortunately, telepathy's AuthenticationFailed error arrives for many
normal cases, like a connection reset during authentication. We cannot
invalidate credentials indiscriminately.

Instead, watch for the two specific wocky errors that indicate the
server probably rejected our credentials and signal only for those.
[telepathy-sasl-signon] Don't attempt to create credentials when signon session fails

This is not relevant for our accounts architecture, and calling
request_password is harmful.