Restructure discovery to have less apps

The apps are not meant to represent MIME types of respective
single file extensions; rather, they represent application/module
that handles several extensions. So this groups extensions under
modules (writer/calc/...). This is required for some WOPI hosts
that whitelist discovery data on per-app base.

The old list of MIME-type-based apps is kept for compatibility
with existing integrations, until they are fixed to use new-style
discovery. Extensions are removed from legacy part, to avoid
duplicating actions.

This also hardcodes content types, to avoid repeated parsing of
discovery.xml.

lint-discovery.py is updated to process new-style information
(ignores legacy part).

Change-Id: Ib8d3518f00510cd0788314d8a9da9a286a52e0ba
Reviewed-on: https://gerrit.libreoffice.org/c/online/+/99637
Tested-by: Jenkins
Tested-by: Jenkins CollaboraOffice <[email protected]>
Reviewed-by: Mike Kaganski <[email protected]>