Move DB from /lib to /usr

I am doing this for 2 reasons:

• The current placement of files is not FHS-compliant. So let's try to follow the standard
• We need this for the /usr merge as approved by the TSC tsc#73 (closed), since doing the transition while holding APK data under /lib is going to be quite error prone

We have decided to move the lock file to /run (already merged in !240 (merged)), after looking at the rationale that moved it to /lib. Executable packages do not carry any state, and are moved to /usr/libexec (part of !238 (merged) included here), else everything else is moved to /usr/lib for FHS compliance. See !203 (comment 437115) for how the transition is planned

In addition, there is also the work to be done to make sure that consumers (currently Discover APK plugin and apk-polkit-server) reload the library when these changes happen, so that they don't think they can lock on /lib/apk/db/lock. But this is not to be solved in this repo