Metadata PR

This PR allows writing keywords (KW) into the supplemental information field of an ISO19115 xml.
For file based KW, an XML file is created at the same location as the KW file. For non-file based KW, the full XML is written into the KW sqlite file.

The XML is generated when KW are written or updated. 

For file based KW, if an XML file is already available, the supplementalInformation tag and it's parents are inserted if missing.
For sqlite based KW, the old dict based record is updated to the new XML based

The used XML template implements only the mandatory fields of ISO19115 and allows setting some defaults values in the InaSAFE settings dialog.