reviewboard: Put config into the local config file

From now on it is required to set review_board.server_url in the local
project configuration file. This URL is used when calling rbt as the
server option (--server).

Story-Id: SF-85
Change-Id: d92934ed63
jira: Configure credentials on per-server basis

From now on the global config format is

  jira:
    credentials:
      - base_prefix: string
        username:    string
        password:    string

When SalsaFlow needs to access JIRA, it looks for the best matching
credentials based on the base_prefix. The best matching credentials are
these where the longest part of the base URL matches.

Story-Id: SF-86
Change-Id: 271adf2a13
wip [ci skip]

Change-Id: 34a4bd1fcb
wip [ci skip]

Change-Id: 4a5feeeec5
wip [ci skip]

Change-Id: 1b2e81f9fc
wip [ci skip]

Change-Id: 706d3a0ee5