ssdp: Don't try to restart SSDP during shutdown
js: Suspend requests during popup windows

Fixes #1973
Revert "skin: Merge all settings during video playback into one list"

This reverts commit 47bf0043201fb679180fe043d72d2e7f97df3644.
playinfo: Fix deadlock

Fixes #1981 (recent regression)
Refactor kvstore a bit

* Add debug support (setting in settings:dev)
* When setting a value to void, delete row from database
Drop stray printf()
kvstore: Improve debugging
prop: Add some more helper funcs

prop_copy()
prop_sub_reemit()
prop_get_int()
Improve video playback settings a quite a bit

Most settings (except subtitle sync offset) are stored in a database
for each video file. In addition to that the user can choose to save
the settings as a default for the current folder the video resides in.
This can be very useful for TV series, etc where the user want to
do some specific changes to the playback config for that particular
set of video items.

In addition to this, it's now also possible to apply the current
configuration as the global configuration

Fixes #1836
Fix build fail
Fix division by zero bug in XMP

Fixes #1978
Terminate all popups when Showtime shuts down

Fixes #1983
smb: Don't block callout thread while waiting for PING response

Fixes #1990