[trunk] Several issues with property pop menu

Setup: rev. 4729; Ubuntu 11.04, Qt SDK 1.1.3 (Qt lib 4.7.3)

Description:

The attached patch fixes 3 issues with the file mscore/mscore/propertymenu.cpp, functions void ScoreView::createElementPropertyMenu() and void ScoreView::elementPropertyAction().

1) No property menu for bar lines: fixed by adding a relevant if at the beginning of createElementPropertyMenu().

2) Command string mismatch between the two functions for time signature property menu ("ts-props" versus "props") made consistent into "ts-props".

3) Command string clash among courtesy time signature, courtesy clefs and courtesy key signatures ("courtesy" in all cases): differentiated into "ts-courtesy", "clef-courtesy" and key-courtesy".

Note: this issue includes and supersedes the older issue at //musescore.org/en/node/11594 .