Mss bugfixes

[rpatters1]

Fix various bugs uncovered as part of the dev process for denigma.

• massage script was adding miscellaneous fields to wrong element
• mss script was calculating pagePrintableWidth incorrectly.
• mss script was setting incorrect bits for underline and strikethru font styles.
• use consistent case for spatium node. (MuseScore has supported the lower case version for a while, even though it does not write it as of 4.4.4.)