Improve PsmfPlayer.

Implement video loop for PsmfPlayer.
Tiny bug fix.
-don't step while the core is active
-reset the counter before starting the core (so that it actually counts the execution time of the last run)
Add EXIT button to new UI
Add UI::EventReturn OnExit
Minor cleanup
sceMpegGetAvcAu should return

PSP_ERROR_MPEG_NO_DATA at first call before mpegAvcDecode.
Match message dialog with real PSP
Minor sizing fix
Merge pull request #2514 from raven02/patch-17

Add EXIT button to new UI
Merge pull request #2520 from raven02/patch-18

Match message dialog with real PSP
Merge pull request #2518 from Kingcom/master

Don't step when the core is active
Add square icon to LOAD/SAVE/DELETE
Merge pull request #2522 from raven02/patch-19

Add Square icon to LOAD/SAVE/DELETE
Match the font size of save dialog with real PSP
Quick fix sizing
Fix wrong YES/NO color of save dialog
Allow the disasm height to be resized a bit more.
Adjust the default disasm height to reduce padding.
Do less memcpy when copying the framebuf to mem.