We refactor the main Aperture service code into a struct that can be
started and stopped. This allows aperture to be used more easily as a library in
other projects.
We update the compile time dependency of lnd to version 0.13.0-beta to
make it easier to run aperture in the same process as other projects
which also updated.
The runtime dependency is still kept at v0.12.0-beta as we don't use any
new RPCs.
To make sure we can capture errors in the challenger's invoice
subscription, we hand the main error channel to the challenger so it can
report back errors on it.
In this commit, we modify our cipher suites and required TLS versions to
allow anything greater than TL 1.1. TLS 1.0 (sslv3) is broken so we
require versions that're safely above that. Without this change, widely
used clients such as `openssl` will fail to connect out to an Aperture
proxy.
In case we use an externally provided certificate (which is created by
an external Let's Encrypt process for example), we don't want to try to
renew it. We identify our own certificates by the organization field we
set.
