metadata: Don't use metadata_source_t for temp storage during queries
metadata: Remove locking during I/O

This should make the metadata UI stuff feel a lot more snappy
xmp: Trig end-of-track after first loop

Fixes #2046
Add missing file
Add some ugly hacks for decoding RGBA lossy jpegs

Fixes #1770
Add some more keymappings

Shift-F7: Seek backwards
Shift-F8: Play/Pause
Shift-F9: Seek forwards
glw/text: Remove dead code
Add new 'image' type and use it for text rendering
Move more stuff into src/image/
Rework image loader / decoding pipeline to be more flexible

Prepares for HW accelerated image manipulation
glw: Get rid of glw_set() vararg attribute setter
glw: Do layout as a specific class callback (instead of signal)

Also start working on conditional refresh
Add conditional rendering of UI

This makes Showtime only redraw UI if needed.

Currently only available on RPI and OSX and needs to be enabled in settings:dev
Make it possible to show/hide sysinfo from menu
search: Add missing prop refs
pool: Fix typo in POOL_BY_MMAP mode
skin: Remove pointless assignment

Fixes #2054
Change severity of "Widget XYZ does not respond to attribute" to DEBUG

refs #2055
prop: Only log 'Refusing to clean prop ...' message when PROP_DEBUG is set

Fixes #2053
glw: Trig UI refresh when scrollbar moves

Fixes #2057