This makes us compatible with mam 6.0

fix #3249

Otherwise, some client won’t do MAM, since they don’t know biboumi supports
it.

[skip ci]

Add a Persistent option on channels

Closes #3230

See merge request !6

fix #3230

ref #3245

ref #3245

ref #3245

Use OBJECT libraries
Remove the louloulibs directory
Write FOUND variables in the cache

cmake: Remove the intermediate static libs

See merge request !7

Should compile faster (and also take less space on disk)

Fix a memory leak that would occur on every DNS request, when using udns

This reverts commit 38ff50f5.