build: move `src/app` to `src/client`
build: create `src/server/main.ml`
lib: create module `Server` and listen on HTTPS
lib: start replying on `/targets` service
build: fix `get-dependencies`

This should make Travis builds work again.
lib: add basic authentication for HTTP requests
lib: improve `/targets` service (“output format”)
lib: add option `archived` to `/targets` service
lib: add server-configuration to `Configuration`
lib: add 3 options to servers' configuration
lib: add daemonization of the server
lib: listen on the “command pipe” (`Server`)
build: make a “test-environment” in `please.sh`
lib: fix `EDSL.run` (was missing env-variables)
test: make “CLI” test not override configuration
doc: add `http_api.md` (for now usage examples)
lib: make sure `/targets` replies only on `GET`
doc: update `http_api.md`
lib: fix command-pipe opening, aesthetically
lib,app: merge client and server applications