fix #34106: problems adding elements to frames

Items added to frames via the context menu were being handled twice - once (incorrectly) by the global code to handle the actions when invoked via main menu or palette, and then again (correctly) by the code specific to the context menu.  This is because the context menus were reusing the global actions.  Bad effects included the scoreview jumping to the top of the first page when adding text to frames on other pages, a spurious additional title frame being created, empty text elements being added to the initial title frame, etc.

I modified the context menu for frames code to borrow the text from the global actions (so take advantage of translation), but to create new actions that trigger only the context menu handling code.

Also, I fixed an issue I found along the way in this same section of code where horizontal frames inserted into vertical frames were much too large, extending off the page.  This seems to have been a typo - initializing the width of the horizontal frame to the width of the scoreview as opposed to the width of the vertical frame.