Dates and versions

[zabak]

As mentioned in #54 it would help to have some date available. In fact, there should be a number of dates and software versions associated with each document and this info should also be downloadable as a metadata set. It should include timestamps of document creation, page upload and every step of the software process. It should always have version info on all the software packages used and its settings. This should be visible in document browser and included in the ALTO files as well to make it downloadable.