JETTY web-sockets client tool

JETTY web-sockets client tool

- Testing tool is place in new module "tools" under "restconf"
  root module and the name of the testtool executable file with
  all dependencies is named ${project.artifactId}
  -${project.version}-executable.
- See ApplicationSettings class for possible input parameters
  of the application as well as the usage. Mandatory parameter is
  stream/s name/s using which the web-socket sessions are
  established. Other parameters can be categorized into two groups:
  1) setup of ping messages (enabled, interval, message)
  2) TLS configuration for WSS streams - keystore, trustore,
     passwords, cipher suites, protocols, ...

JIRA: NETCONF-623
Change-Id: Ifaf340ee1e0ba26c203bb1c663588cc94fb5496d
Signed-off-by: Jaroslav Tóth <jtoth@frinx.io>
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>