In successive commits we want to access lnrpc specifc methods
and objects, so here we import github.com/lightningnetwork/lnd v0.20.1-beta
into looprpc and update relevant versions.
Bump the minimum golang version to 1.15 in the go.mod file. The go
version is also updated in the Dockerfile and travis.yml file. This is
required so that the correct `errors.Is` method is used.
* Introduced docker integration
* Added Dockerfile to build loopd and loop with no dependencies.
* Added instructions to build and run docker image.
* Fixed documentation on mapping of ~/.lnd
* Would have caused problems because ~/.loop wasn't mapped
* Now map entire home directory
* Updated DOCKER.md example to just map ~/.lnd and ~/.loop.
* Removed mapping of home directory - one of the benefits of docker is being explicit about the resources the container uses so I felt bad mapping the entire home directory when only two known folders were used.
