browsertests for some extensions

Should really use shell scripts instead.

cucumber is instructed to use the 'ciwmf' profile, letting author finely
tweak the settings.  We always skip tests tagged '@phantomjs-bug' though
since that is the browser we are using.

The MEDIAWIKI_URL needs 'index.php?title=' since there is no pathinfo
setup on the local wiki.

Creates jobs:

    mwext-browsertests-MobileFrontend-phantomjs
    mwext-browsertests-Translatewiki-phantomjs
    mwext-browsertests-UniversalLanguageSelector-phantomjs
    mwext-browsertests-VisualEditor-phantomjs

Change-Id: I4e7da6628395ab8eebb9cbd6a0a60d3f33759b18