Added support for https and basepath parameters for youtrack.

The script now supports the environment variable `HUBOT_YOUTRACK_URL`
which has to follow the format:

    <scheme>://<username>:<password>@<host:port>/<basepath>

The basepath part is optional. If the variable is not set the old
variables of the script are used. Therefore there should be no migration
issues.
Removed regular expression and use url.parse for the url.

Fixed a small bug regarding the path in `askYoutrack`.
Merge pull request #1098 from jan0sch/youtrack

Added support for https and basepath parameters for youtrack.
Removed duplicated doc line
Merge pull request #1103 from morgoth/patch-1

Removed duplicated doc line
Merge remote-tracking branch 'upstream/master'