Extract printing metadata into its own file

This simplifies dealing with inclusion for printing only.
The BEK-standalone binary needs to print metadata from the .BEK
file, there's no need for other parsing functions.
Bugfix: Date was not correctly displayed

When printing human-readable date from a dataset timestamp, the
format printing conflited with the timestamp we where trying to
print.
Clean read_bekfile* files and standalone

Mainly avoid duplicate code.