installation: location of plupload

* Updates location from where to download plupload to local hosting
  on invenio-software.org site.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
Travis CI: initial release of configuration

* Forward-ported from 5b6225743b2f74344053f33dc70562675d360a3d
  so that there is no need to wait for the following big
  master-to-next merge in order to have working Travis CI
  configuration in the next branch.

* NOTE Removes regression testing part which is not yet next ready.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>