present in meson but not in autotools and causes linking errors

Signed-off-by: Christopher Degawa <ccom@randomderp.com>

I'm not 100% sure the failures are false positive but they look like so

Fixes #292

refs #292

refs #292

Refs #292

UPDATE FROM was introduced in 3.33.0 and we'll need it in next commit

refs #292

We now store the numbre of media per-type, and the number of present
media, per-type as well.
refs #292

We'll soon need to track media regardless of their presence, depending
on the query passed by the caller
refs #292

refs #292

refs #292

refs #292

refs #292

We need to filter artists with at least a single track even when using
ArtistIncluded::All, otherwise we might end up returning unknown and
various artists even if they have no tracks

refs #292

refs #292

refs #292

We need a more up to date meson version to build the extra test programs
since they as they are not built by default

We only include the test subdir when libvlc is enabled & found

This shouldn't be needed but for now meson will build the test
executables by default, including when they are explicitely tagged with
'build_by_default: false'

Don't even attempt to detect libjpeg if we know it won't be used. If it
is needed, try to use pkg-config, and then fallback to manual search
with a libjpeg_prefix option.

Use a filelock ml.lock in the medialib folder path to guarantee that
only one instance of the medialib can be running for this database.

Split initialize() in two parts:
 1. set the db path and ml folder path
 2. initialize the database

This paves the way to implement single medialib instance in the first
step while keeping the actual initialization lazy.