Initial integration of KnpMenu

Visible locations below the root one with a content class listed in
legacy's menu.ini[MenuContentSettings.TopIdentifierList] are returned.
Made travis.yml more flexible

The ezpublish-community branch can now easily be changed in the git clone command line.
[tmp] changed ezp-community branch for travis
Merge pull request #99 from ezsystems/EZP-22601-KnpMenu

Initial KnpMenuBundle integration