Simpler mastersnippet parsing

[kakwok]

Supersade #211, will include also #285. Almost ready to go. List of testings done and ToDO here:

Checked items:

1. Port snippet script works: (Need to add schema to mastersnippet node, update old tag names)
2. Feature: Parse commonMS before main MS
3. Feature: Main MS over-rides commonMS item
4. Parsed new parameter
5. Fail gracefully when unknown parameter is found

To-Do:
2. LV2 parses MS and commonMS
3. Save MS and commonMS as FM parameter
4. Protect FM parameters
5. Test VectorT/MapT parameter
6. Suppress TCDS printing statement
7. Update portScript to remove NumberOfEvent from Mastersnippet
8. Check the default overwrite feature.
9. Make sure FedEnableMask is ignored in global

[kakwok]

Update checklist:

1. Port snippet script works: (Need to add schema to mastersnippet node, update old tag names)
2. Feature: Parse commonMS before main MS
3. Feature: Main MS over-rides commonMS item
4. Parsed new parameter
5. Fail gracefully when unknown parameter is found
6. LV2readMaster (done in Lv2 reads master #363 )
7. Suppress TCDS printing statement (done in 93d15e0)
8. Update portScript to remove NumberOfEvent from Mastersnippet (done in 46660d2)

To-Do:
3. Save MS and commonMS as FM parameter (to be done in other PR)
4. Protect FM parameters (to be done with #384 )
5. Test VectorT/MapT parameter
8. Check the default overwrite feature.
9. Make sure FedEnableMask is ignored in global