Index third party apps that do not ship as.xml data about appstream

[ximion]

We could add these apps as stub and have the software center figure out the package which owns them via PK GetFiles(), since doing calls to the package management system is something I don't want to do when updating the cache - this process should be as fast as possible and should be able to run at any time (even if the package database is locked or being updated).

This solution is really ugly, because it will introduce entries without installation candidate into the AppStream database, which currently does never happen. But this might be a bitter pill to take, if there is strong demand from software center people to add this feature.

[ximion]

With the latest changes, we might finally be able to do this...
Problem is: Do we want to do this? It will force software-center apps to resolve a filename to packages, which is pretty slow...

[ximion]

I think I found a solution for this issue which makes sense (using a configuration option to switch to "show data from metainfo files" mode for developers, and reading .desktop files and metainfo files unconditionally if the distributor does not have any information about them).
Will work on this for a later release (maybe 0.10.2)