More functionality to loops

Feature Request

Part 1
1. Make the Loop "start" marker an editable object.
add a propperty "NumberOfLoops"

when the tune is played respect the numbers of loops stored in the marker.
(if it is zero, loop endless as it is now)

Part 2
1. When exporting the tune to an audio format flac, wave, mp3, mid etc.
check if a loop is active. If it is then export the loop from "start" marker to "end" marker and respect the NumberOfLoops

This should give you a Audio file with the score NumberOfLoops times repeated.
Neatly without any gaps between the loops.

Why:
This resembles closely the ABC Tag P:(AB)5 which playes Part A,then Part B, and repeat it 5 times If the Tag P:(AB)5 is in effect, it will also do a looped export to audio.

So if there is no loop set in Musescore while exporting to audio file, export the score only once.